The Relation Between Magnetic Fields and X-ray Emission for Solar Microflares and Active Regions

NASA Astrophysics Data System (ADS)

Kirichenko, A. S.; Bogachev, S. A.

2017-09-01

We present the result of a comparison between magnetic field parameters and the intensity of X-ray emission for solar microflares with Geosynchronous Operational Environmental Satellites (GOES) classes from A0.02 to B5.1. For our study, we used the monochromatic MgXII Imaging Spectroheliometer (MISH), the Full-disk EUV Telescope (FET), and the Solar PHotometer in X-rays (SphinX) instruments onboard the Complex Orbital Observations Near-Earth of Activity of the Sun-Photon CORONAS- Photon spacecraft because of their high sensitivity in soft X-rays. The peak flare flux (PFF) for solar microflares was found to depend on the strength of the magnetic field and on the total unsigned magnetic flux as a power-law function. In the spectral range 2.8 - 36.6 Å, which shows very little increase related to microflares, the power-law index of the relation between the X-ray flux and magnetic flux for active regions is 1.48 ±0.86, which is close to the value obtained previously by Pevtsov et al. ( Astrophys. J. 598, 1387, 2003) for different types of solar and stellar objects. In the spectral range 1 - 8 Å, the power-law indices for PFF(B) and PFF(Φ) for microflares are 3.87 ±2.16 and 3 ±1.6, respectively. We also make suggestions on the heating mechanisms in active regions and microflares under the assumption of loops with constant pressure and heating using the Rosner-Tucker-Vaiana scaling laws.

A HELIOSEISMIC SURVEY OF NEAR-SURFACE FLOWS AROUND ACTIVE REGIONS AND THEIR ASSOCIATION WITH FLARES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braun, D. C., E-mail: dbraun@cora.nwra.com

We use helioseismic holography to study the association of shallow flows with solar flare activity in about 250 large sunspot groups observed between 2010 and 2014 with the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. Four basic flow parameters: horizontal speed, horizontal component of divergence, vertical component of vorticity, and a vertical kinetic helicity proxy, are mapped for each active region (AR) during its passage across the solar disk. Flow indices are derived representing the mean and standard deviation of these parameters over magnetic masks and compared with contemporary measures of flare X-ray flux. A correlation exists formore » several of the flow indices, especially those based on the speed and the standard deviation of all flow parameters. However, their correlation with X-ray flux is similar to that observed with the mean unsigned magnetic flux density over the same masks. The temporal variation of the flow indices are studied, and a superposed epoch analysis with respect to the occurrence to 70 M and X-class flares is made. While flows evolve with the passage of the ARs across the disk, no discernible precursors or other temporal changes specifically associated with flares are detected.« less

Diagnostics of Turbulent Dynamo from the Flux Emergence Rate in Solar Active Regions

NASA Astrophysics Data System (ADS)

Abramenko, V. I.; Tikhonova, O. I.; Kutsenko, A. S.

2017-12-01

Line-of-sight magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO) and by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) for 14 emerging ARs were used to study the derivative of the total unsigned flux-the flux emergence rate, R( t). We found that the emergence regime is not universal: each AR displays a unique emergence process. Nevertheless, two types of the emergence process can be identified. First type is a "regular" emergence with quasi-constant behavior of R( t) during a 1-3 day emergence interval with a rather low magnitude of the flux derivative, R max = (0.57 ± 0.22) × 1022 Mx day-1. The second type can be described as "accelerated" emergence with a long interval (>1 day) of the rapidly increasing flux derivative R( t) that result in a rather high magnitude of R max= (0.92 ± 0.29) × 1022 Mx day-1, which later changes to a very short (about a one third of day) interval of R( t) = const followed by a monotonous decrease of R( t). The first type events might be associated with emergence of a flux tube with a constant amount of flux that rises through the photosphere with a quasi-constant speed. Such events can be explained by the traditional largescale solar dynamo generating the toroidal flux deep in the convective zone. The second-type events can be interpreted as a signature of sub-surface turbulent dynamo action that generates additional magnetic flux (via turbulent motions) as the magnetic structure makes its way up to the solar surface.

Solar photospheric network properties and their cycle variation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thibault, K.; Charbonneau, P.; Béland, M., E-mail: kim@astro.umontreal.ca-a, E-mail: paulchar@astro.umontreal.ca-b, E-mail: michel.beland@calculquebec.ca-c

We present a numerical simulation of the formation and evolution of the solar photospheric magnetic network over a full solar cycle. The model exhibits realistic behavior as it produces large, unipolar concentrations of flux in the polar caps, a power-law flux distribution with index –1.69, a flux replacement timescale of 19.3 hr, and supergranule diameters of 20 Mm. The polar behavior is especially telling of model accuracy, as it results from lower-latitude activity, and accumulates the residues of any potential modeling inaccuracy and oversimplification. In this case, the main oversimplification is the absence of a polar sink for the flux,more » causing an amount of polar cap unsigned flux larger than expected by almost one order of magnitude. Nonetheless, our simulated polar caps carry the proper signed flux and dipole moment, and also show a spatial distribution of flux in good qualitative agreement with recent high-latitude magnetographic observations by Hinode. After the last cycle emergence, the simulation is extended until the network has recovered its quiet Sun initial condition. This permits an estimate of the network relaxation time toward the baseline state characterizing extended periods of suppressed activity, such as the Maunder Grand Minimum. Our simulation results indicate a network relaxation time of 2.9 yr, setting 2011 October as the soonest the time after which the last solar activity minimum could have qualified as a Maunder-type Minimum. This suggests that photospheric magnetism did not reach its baseline state during the recent extended minimum between cycles 23 and 24.« less

Speed of CMEs and the Magnetic Non-Potentiality of their Source Active Regions

NASA Technical Reports Server (NTRS)

Tiwari, Sanjiv Kumar; Falconer, David Allen; Moore, Ronald L.; Venkatakrishnan, P.; Winebarger, Amy R.; Khazanov, Igor G.

2014-01-01

Most fast coronal mass ejections (CMEs) originate from solar active regions (ARs). Non-potentiality of ARs plausibly determines the speed of CMEs in the outer corona. Several other unexplored parameters might be important as well. To find out the relation between the intial speed of CMEs and the non-potentiality of source ARs, we identified over a hundred of CMEs with source ARs via their co-produced flares. The speed of the CMEs are collected from the SOHO LASCO CME catalog. We have used vector magnetograms obtained with HMI/SDO, to evaluate various magnetic non-potentiality parameters, e.g. magnetic free-energy proxies, twist, shear angle, signed shear angle, net current etc. We have also included several other parameters e.g. total unsigned flux, magnetic area of ARs, area of sunspots, to investigate their correlation, if any, with the initial speeds of CMEs. Our preliminary results show that the ARs with larger non-potentiality and area produce faster CMEs but they can also produce slow ones. The ARs with lesser non-potentiality and area generally produce only slower CMEs.

MAGNETIC ENERGY SPECTRA IN SOLAR ACTIVE REGIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abramenko, Valentyna; Yurchyshyn, Vasyl

Line-of-sight magnetograms for 217 active regions (ARs) with different flare rates observed at the solar disk center from 1997 January until 2006 December are utilized to study the turbulence regime and its relationship to flare productivity. Data from the SOHO/MDI instrument recorded in the high-resolution mode and data from the BBSO magnetograph were used. The turbulence regime was probed via magnetic energy spectra and magnetic dissipation spectra. We found steeper energy spectra for ARs with higher flare productivity. We also report that both the power index, {alpha}, of the energy spectrum, E(k) {approx} k{sup -}{alpha}, and the total spectral energy,more » W = {integral}E(k)dk, are comparably correlated with the flare index, A, of an AR. The correlations are found to be stronger than those found between the flare index and the total unsigned flux. The flare index for an AR can be estimated based on measurements of {alpha} and W as A = 10{sup b}({alpha}W){sup c}, with b = -7.92 {+-} 0.58 and c = 1.85 {+-} 0.13. We found that the regime of the fully developed turbulence occurs in decaying ARs and in emerging ARs (at the very early stage of emergence). Well-developed ARs display underdeveloped turbulence with strong magnetic dissipation at all scales.« less

On the Detection of Coronal Dimmings and the Extraction of Their Characteristic Properties

NASA Astrophysics Data System (ADS)

Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova, T.; Vanninathan, K.

2018-03-01

Coronal dimmings are distinct phenomena associated with coronal mass ejections (CMEs). The study of coronal dimmings and the extraction of their characteristic parameters help us to obtain additional information regarding CMEs, especially on the initiation and early evolution of Earth-directed CMEs. We present a new approach to detect coronal dimming regions based on a thresholding technique applied on logarithmic base-ratio images. Characteristic dimming parameters describing the dynamics, morphology, magnetic properties, and the brightness of coronal dimming regions are extracted by cumulatively summing newly dimmed pixels over time. It is also demonstrated how core dimming regions are identified as a subset of the overall identified dimming region. We successfully apply our method to two well-observed coronal dimming events. For both events, the core dimming regions are identified and the spatial evolution of the dimming area reveals the expansion of the dimming region around these footpoints. We also show that in the early impulsive phase of the dimming expansion the total unsigned magnetic flux involved in the dimming regions is balanced and that up to 30% of this flux results from the localized core dimming regions. Furthermore, the onset in the profile of the area growth rate is cotemporal with the start of the associated flares and in one case also with the fast rise of the CME, indicating a strong relationship of coronal dimmings with both flares and CMEs.

Solar Flare Prediction Model with Three Machine-learning Algorithms using Ultraviolet Brightening and Vector Magnetograms

NASA Astrophysics Data System (ADS)

Nishizuka, N.; Sugiura, K.; Kubo, Y.; Den, M.; Watari, S.; Ishii, M.

2017-02-01

We developed a flare prediction model using machine learning, which is optimized to predict the maximum class of flares occurring in the following 24 hr. Machine learning is used to devise algorithms that can learn from and make decisions on a huge amount of data. We used solar observation data during the period 2010-2015, such as vector magnetograms, ultraviolet (UV) emission, and soft X-ray emission taken by the Solar Dynamics Observatory and the Geostationary Operational Environmental Satellite. We detected active regions (ARs) from the full-disk magnetogram, from which ˜60 features were extracted with their time differentials, including magnetic neutral lines, the current helicity, the UV brightening, and the flare history. After standardizing the feature database, we fully shuffled and randomly separated it into two for training and testing. To investigate which algorithm is best for flare prediction, we compared three machine-learning algorithms: the support vector machine, k-nearest neighbors (k-NN), and extremely randomized trees. The prediction score, the true skill statistic, was higher than 0.9 with a fully shuffled data set, which is higher than that for human forecasts. It was found that k-NN has the highest performance among the three algorithms. The ranking of the feature importance showed that previous flare activity is most effective, followed by the length of magnetic neutral lines, the unsigned magnetic flux, the area of UV brightening, and the time differentials of features over 24 hr, all of which are strongly correlated with the flux emergence dynamics in an AR.

Solar Flare Prediction Model with Three Machine-learning Algorithms using Ultraviolet Brightening and Vector Magnetograms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishizuka, N.; Kubo, Y.; Den, M.

We developed a flare prediction model using machine learning, which is optimized to predict the maximum class of flares occurring in the following 24 hr. Machine learning is used to devise algorithms that can learn from and make decisions on a huge amount of data. We used solar observation data during the period 2010–2015, such as vector magnetograms, ultraviolet (UV) emission, and soft X-ray emission taken by the Solar Dynamics Observatory and the Geostationary Operational Environmental Satellite . We detected active regions (ARs) from the full-disk magnetogram, from which ∼60 features were extracted with their time differentials, including magnetic neutralmore » lines, the current helicity, the UV brightening, and the flare history. After standardizing the feature database, we fully shuffled and randomly separated it into two for training and testing. To investigate which algorithm is best for flare prediction, we compared three machine-learning algorithms: the support vector machine, k-nearest neighbors (k-NN), and extremely randomized trees. The prediction score, the true skill statistic, was higher than 0.9 with a fully shuffled data set, which is higher than that for human forecasts. It was found that k-NN has the highest performance among the three algorithms. The ranking of the feature importance showed that previous flare activity is most effective, followed by the length of magnetic neutral lines, the unsigned magnetic flux, the area of UV brightening, and the time differentials of features over 24 hr, all of which are strongly correlated with the flux emergence dynamics in an AR.« less

Connecting Coronal Mass Ejections to Their Solar Active Region Sources: Combining Results from the HELCATS and FLARECAST Projects

NASA Astrophysics Data System (ADS)

Murray, Sophie A.; Guerra, Jordan A.; Zucca, Pietro; Park, Sung-Hong; Carley, Eoin P.; Gallagher, Peter T.; Vilmer, Nicole; Bothmer, Volker

2018-04-01

Coronal mass ejections (CMEs) and other solar eruptive phenomena can be physically linked by combining data from a multitude of ground-based and space-based instruments alongside models; however, this can be challenging for automated operational systems. The EU Framework Package 7 HELCATS project provides catalogues of CME observations and properties from the Heliospheric Imagers on board the two NASA/STEREO spacecraft in order to track the evolution of CMEs in the inner heliosphere. From the main HICAT catalogue of over 2,000 CME detections, an automated algorithm has been developed to connect the CMEs observed by STEREO to any corresponding solar flares and active-region (AR) sources on the solar surface. CME kinematic properties, such as speed and angular width, are compared with AR magnetic field properties, such as magnetic flux, area, and neutral line characteristics. The resulting LOWCAT catalogue is also compared to the extensive AR property database created by the EU Horizon 2020 FLARECAST project, which provides more complex magnetic field parameters derived from vector magnetograms. Initial statistical analysis has been undertaken on the new data to provide insight into the link between flare and CME events, and characteristics of eruptive ARs. Warning thresholds determined from analysis of the evolution of these parameters is shown to be a useful output for operational space weather purposes. Parameters of particular interest for further analysis include total unsigned flux, vertical current, and current helicity. The automated method developed to create the LOWCAT catalogue may also be useful for future efforts to develop operational CME forecasting.

Correlation between solar flare productivity and photospheric vector magnetic fields

NASA Astrophysics Data System (ADS)

Cui, Yanmei; Wang, Huaning

2008-11-01

Studying the statistical correlation between the solar flare productivity and photospheric magnetic fields is very important and necessary. It is helpful to set up a practical flare forecast model based on magnetic properties and improve the physical understanding of solar flare eruptions. In the previous study ([Cui, Y.M., Li, R., Zhang, L.Y., He, Y.L., Wang, H.N. Correlation between solar flare productivity and photospheric magnetic field properties 1. Maximum horizontal gradient, length of neutral line, number of singular points. Sol. Phys. 237, 45 59, 2006]; from now on we refer to this paper as ‘Paper I’), three measures of the maximum horizontal gradient, the length of the neutral line, and the number of singular points are computed from 23990 SOHO/MDI longitudinal magnetograms. The statistical relationship between the solar flare productivity and these three measures is well fitted with sigmoid functions. In the current work, the three measures of the length of strong-shear neutral line, total unsigned current, and total unsigned current helicity are computed from 1353 vector magnetograms observed at Huairou Solar Observing Station. The relationship between the solar flare productivity and the current three measures can also be well fitted with sigmoid functions. These results are expected to be beneficial to future operational flare forecasting models.

A Survey of Nanoflare Properties in Solar Active Regions

NASA Astrophysics Data System (ADS)

Viall, N. M.; Klimchuk, J. A.

2013-12-01

We investigate coronal heating using a systematic technique to analyze the properties of nanoflares in active regions (AR). Our technique computes cooling times, or time-lags, on a pixel-by-pixel basis using data taken with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. Our technique has the advantage that it allows us to analyze all of the coronal AR emission, including the so-called diffuse emission. We recently presented results using this time-lag analysis on NOAA AR 11082 (Viall & Klimchuk 2012) and found that the majority of the pixels contained cooling plasma along their line of sight, consistent with impulsive coronal nanoflare heating. Additionally, our results showed that the nanoflare energy is stronger in the AR core and weaker in the active region periphery. Are these results representative of the nanoflare properties exhibited in the majority of ARs, or is AR 11082 unique? Here we present the time-lag results for a survey of ARs and show that these nanoflare patterns are born out in other active regions, for a range of ages, magnetic complexity, and total unsigned magnetic flux. Other aspects of the nanoflare properties, however, turn out to be dependent on certain AR characteristics.

Long-term magnetic field monitoring of the Sun-like star ξ Bootis A

NASA Astrophysics Data System (ADS)

Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin, J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.; Théado, S.; Van Grootel, V.

2012-04-01

Aims: We aim to investigate the long-term temporal evolution of the magnetic field of the solar-type star ξ Bootis A, both from direct magnetic field measurements and from the simultaneous estimate of indirect activity indicators. Methods: We obtained seven epochs of high-resolution, circularly-polarized spectra from the NARVAL spectropolarimeter between 2007 and 2011, for a total of 76 spectra. Using approximately 6100 photospheric spectral lines covering the visible domain, we employed a cross-correlation procedure to compute a mean polarized line profile from each spectrum. The large-scale photospheric magnetic field of the star was then modelled by means of Zeeman-Doppler Imaging, allowing us to follow the year-to-year evolution of the reconstructed magnetic topology. Simultaneously, we monitored the width of several magnetically sensitive spectral lines, the radial velocity, the line asymmetry of intensity line profiles, and the chromospheric emission in the cores of the Ca II H and Hα lines. Results: During the highest observed activity states, in 2007 and 2011, the large-scale field of ξ Bootis A is almost completely axisymmetric and is dominated by its toroidal component. The toroidal component persists with a constant polarity, containing a significant fraction of the magnetic energy of the large-scale surface field through all observing epochs. The magnetic topologies reconstructed for these activity maxima are very similar, suggesting a form of short cyclicity in the large-scale field distribution. The mean unsigned large-scale magnetic flux derived from the magnetic maps varies by a factor of about 2 between the lowest and highest observed magnetic states. The chromospheric flux is less affected and varies by a factor of 1.2. Correlated temporal evolution, due to both rotational modulation and seasonal variability, is observed between the Ca II emission, the Hα emission and the width of magnetically sensitive lines. The rotational dependence of polarimetric magnetic measurements displays a weak correlation with other activity proxies, presumably due to the different spatial scales and centre-to-limb darkening associated with polarimetric signatures, as compared to non-polarized activity indicators. Better agreement is observed on the longer term. When measurable, the differential rotation reveals a strong latitudinal shear in excess of 0.2 rad d-1. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France.Tables 3-6 are available in electronic form at http://www.aanda.org

Unsignaled Delay of Reinforcement, Relative Time, and Resistance to Change

ERIC Educational Resources Information Center

Shahan, Timothy A.; Lattal, Kennon A.

2005-01-01

Two experiments with pigeons examined the effects of unsignaled, nonresetting delays of reinforcement on responding maintained by different reinforcement rates. In Experiment 1, 3-s unsignaled delays were introduced into each component of a multiple variable-interval (VI) 15-s VI 90-s VI 540-s schedule. When considered as a proportion of the…

Algorithms for sorting unsigned linear genomes by the DCJ operations.

PubMed

Jiang, Haitao; Zhu, Binhai; Zhu, Daming

2011-02-01

The double cut and join operation (abbreviated as DCJ) has been extensively used for genomic rearrangement. Although the DCJ distance between signed genomes with both linear and circular (uni- and multi-) chromosomes is well studied, the only known result for the NP-complete unsigned DCJ distance problem is an approximation algorithm for unsigned linear unichromosomal genomes. In this article, we study the problem of computing the DCJ distance on two unsigned linear multichromosomal genomes (abbreviated as UDCJ). We devise a 1.5-approximation algorithm for UDCJ by exploiting the distance formula for signed genomes. In addition, we show that UDCJ admits a weak kernel of size 2k and hence an FPT algorithm running in O(2(2k)n) time.

Multiscale Architectures and Parallel Algorithms for Video Object Tracking

DTIC Science & Technology

2011-10-01

0 4 : if FIFO1 contains nDt frames then 5: Partition data into blocks. 6: Put SPE control block information...char buf 4 = FF; vec to r unsigned char buf 5 = FF; vec to r unsigned char buf 6 = FF; vec to r unsigned char buf 7 = FF; for ( j = 0 ; j < s i z e ; j...Public Release; Distribution Unlimited 8 7 u 6 ill :J (;) 5 E -;::; c 0 4 ~ u Q) X 3 Q) 8 7 6 u Q) Ul 5 :J (;) E :;::; 4 c 0

Safety and Guidelines for Marked and Unmarked Pedestrian Crosswalks at Unsignalized Intersections in Nevada

DOT National Transportation Integrated Search

2012-09-01

This report examines two aspects of marked and unmarked crosswalks at unsignalized intersections. Firstly, the report assesses the safety performance of marked/unmarked crosswalks in Nevada through comparing pedestrian-related crash rates. In which, ...

10. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

10. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, Courtesy, The Cosmos Club PROPOSED FLOOR PLANS, 2121 MASSACHUSETTS AVENUE, N.W., BLUEPRINT #11, THIRD FLOOR PLAN - Townsend House, 2121 Massachusetts Avenue Northwest, Washington, District of Columbia, DC

11. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, Courtesy, The Cosmos Club PROPOSED FLOOR PLANS, 2121 MASSACHUSETTS AVENUE, N.W., BLUEPRINT #11, FOURTH FLOOR PLAN - Townsend House, 2121 Massachusetts Avenue Northwest, Washington, District of Columbia, DC

9. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

9. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, Courtesy, The Cosmos Club PROPOSED FLOOR PLANS, 2121 MASSACHUSETTS AVENUE, N.W., BLUEPRING #11, SECOND FLOOR PLAN - Townsend House, 2121 Massachusetts Avenue Northwest, Washington, District of Columbia, DC

8. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

8. Historic American Buildings Survey Photocopy of Unsigned, Undated Drawing, Courtesy, The Cosmos Club PROPOSED FLOOR PLANS, 2121 MASSACHUSETTS AVENUE, N.W., BLUEPRINT #11, FIRST-FLOOR PLAN - Townsend House, 2121 Massachusetts Avenue Northwest, Washington, District of Columbia, DC

Safety effects of unsignalized superstreets in North Carolina.

PubMed

Ott, Sarah E; Haley, Rebecca L; Hummer, Joseph E; Foyle, Robert S; Cunningham, Christopher M

2012-03-01

Arterials across the United States are experiencing far too many collisions. Agencies tasked with improving these arterials have few available effective solutions. Superstreets, called restricted crossing u-turns by the Federal Highway Administration (FHWA), are part of a menu of unconventional arterial intersection designs that may provide a promising solution. Up to this point, there is little valid information available on the safety effects of superstreets, as study results have been from basic analyses that only account for traffic volume changes. The purpose of this research was to determine the safety effects of the unsignalized superstreet countermeasure on existing arterials in North Carolina. The safety study involved traffic flow adjustment, comparison-group, and Empirical Bayes analyses of 13 unsignalized superstreet intersections in North Carolina. The superstreets have been installed in the last few years across the state as opportunities presented themselves, but not necessarily at the most hazardous sites. The unsignalized superstreet countermeasure showed a significant reduction in total, angle and right turn, and left turn collisions in all analyses. Analyses also showed a significant reduction in fatal and injury collisions. The authors recommend that future analysts use a crash modification factor of 46 percent when considering the conversion of a typical unsignalized arterial intersection into a superstreet. Copyright © 2011 Elsevier Ltd. All rights reserved.

Developing a short range vehicle to infrastructure communication system to enhance the safety at STOP sign intersections : final report.

DOT National Transportation Integrated Search

2016-05-01

Stop sign controlled unsignalized intersections raise a public safe concern. Even though various strategies, such as engineering, education, and policy, have been applied in practice, there are a number of fatal crashes occurred at unsignalized inter...

Contingency Tracking during Unsignaled Delayed Reinforcement

ERIC Educational Resources Information Center

Keely, Josue; Feola, Tyler; Lattal, Kennon A.

2007-01-01

Three experiments were conducted with rats in which responses on one lever (labeled the functional lever) produced reinforcers after an unsignaled delay period that reset with each response during the delay. Responses on a second, nonfunctional, lever did not initiate delays, but, in the first and third experiments, such responses during the last…

Resistance to Change of Responding Maintained by Unsignaled Delays to Reinforcement: A Response-Bout Analysis

ERIC Educational Resources Information Center

Podlesnik, Christopher A.; Jimenez-Gomez, Corina; Ward, Ryan D.; Shahan, Timothy A.

2006-01-01

Previous experiments have shown that unsignaled delayed reinforcement decreases response rates and resistance to change. However, the effects of different delays to reinforcement on underlying response structure have not been investigated in conjunction with tests of resistance to change. In the present experiment, pigeons responded on a…

Signaled and Unsignaled Terminal Links in Concurrent Chains I: Effects of Reinforcer Probability and Immediacy

ERIC Educational Resources Information Center

Mattson, Karla M.; Hucks, Andrew; Grace, Randolph C.; McLean, Anthony P.

2010-01-01

Eight pigeons responded in a three-component concurrent-chains procedure, with either independent or dependent initial links. Relative probability and immediacy of reinforcement in the terminal links were both varied, and outcomes on individual trials (reinforcement or nonreinforcement) were either signaled or unsignaled. Terminal-link fixed-time…

Context Blocking in Rat Autoshaping: Sign-Tracking versus Goal-Tracking

ERIC Educational Resources Information Center

Costa, Daniel S. J.; Boakes, Robert A.

2009-01-01

Prior experience of unsignaled food can interfere with subsequent acquisition by birds of autoshaped key-pecking at a signal light. This has been understood to indicate that unsignaled food results in context conditioning, which blocks subsequent learning about the keylight-food relationship. In the present experiment with rats lever insertion as…

Analysis of Crossing Speed of the Pedestrians in Marked and Unmarked Crosswalks in the Signalized and Un-Signalized Intersections (Case Study: Rasht city)

NASA Astrophysics Data System (ADS)

Behbahani, Hamid; Najafi Moghaddam Gilani, Vahid; Jahangir Samet, Mehdi; Salehfard, Reza

2017-10-01

Pedestrians affect the traffic in the signalized and un-signalized intersections. Therefore, identifying the behavioural features of the pedestrians is of great importance and may result in better designing facilities for them. In this study, by shooting the four intersections in Rasht for 15 hours and inventory from 4568 pedestrians, crossing speed of the pedestrians in the marked crosswalks and unmarked crosswalks was evaluated and analysed. Results showed that pedestrians‧ crossing speed in the marked crosswalks is higher than their crossing speed in the unmarked crosswalks in both signalized and un-signalized intersections. Moreover, in the unmarked crosswalks in the signalized intersections, 15th percentile speed of male pedestrians, female pedestrians and group of pedestrians’ decrease 6.4%, 5.4% and 12.2%, respectively, compared with the 15th percentile speed in the marked crosswalks. Above-mentioned values in the unmarked crosswalks in the un-signalized intersections for male pedestrians, female pedestrians, and group of pedestrians decrease 1.2%, 3.8%, and 1.4%, respectively.

A Generalized DIF Effect Variance Estimator for Measuring Unsigned Differential Test Functioning in Mixed Format Tests

ERIC Educational Resources Information Center

Penfield, Randall D.; Algina, James

2006-01-01

One approach to measuring unsigned differential test functioning is to estimate the variance of the differential item functioning (DIF) effect across the items of the test. This article proposes two estimators of the DIF effect variance for tests containing dichotomous and polytomous items. The proposed estimators are direct extensions of the…

Evaluation of fixed momentary dro schedules under signaled and unsignaled arrangements.

PubMed

Hammond, Jennifer L; Iwata, Brian A; Fritz, Jennifer N; Dempsey, Carrie M

2011-01-01

Fixed momentary schedules of differential reinforcement of other behavior (FM DRO) generally have been ineffective as treatment for problem behavior. Because most early research on FM DRO included presentation of a signal at the end of the DRO interval, it is unclear whether the limited effects of FM DRO were due to (a) the momentary response requirement of the schedule per se or (b) discrimination of the contingency made more salient by the signal. To separate these two potential influences, we compared the effects of signaled versus unsignaled FM DRO with 4 individuals with developmental disabilities whose problem behavior was maintained by social-positive reinforcement. During signaled FM DRO, the experimenter presented a visual stimulus 3 s prior to the end of the DRO interval and delivered reinforcement contingent on the absence of problem behavior at the second the interval elapsed. Unsignaled DRO was identical except that interval termination was not signaled. Results indicated that signaled FM DRO was effective in decreasing 2 subjects' problem behavior, whereas an unsignaled schedule was required for the remaining 2 subjects. These results suggest that the response requirement per se of FM DRO may not be problematic if it is not easily discriminated.

An extended car-following model at un-signalized intersections under V2V communication environment

PubMed Central

Wang, Tao; Li, Peng

2018-01-01

An extended car-following model is proposed in this paper to analyze the impacts of V2V (vehicle to vehicle) communication on the micro driving behavior at the un-signalized intersection. A four-leg un-signalized intersection with twelve streams (left-turn, through movement, and right turn from each leg) is used. The effect of the guidance strategy on the reduction of the rate of stops and total delay is explored by comparing the proposed model and the traditional FVD car-following model. The numerical results illustrate that potential conflicts between vehicles can be predicted and some stops can be avoided by decelerating in advance. The driving comfort and traffic efficiency can be improved accordingly. More benefits could be obtained under the long communication range, low to medium traffic density, and simple traffic pattern conditions. PMID:29425243

Linear magnetic motor/generator. [to generate electric energy using magnetic flux for spacecraft power supply

NASA Technical Reports Server (NTRS)

Studer, P. A. (Inventor)

1982-01-01

A linear magnetic motor/generator is disclosed which uses magnetic flux to provide mechanical motion or electrical energy. The linear magnetic motor/generator includes an axially movable actuator mechanism. A permament magnet mechanism defines a first magnetic flux path which passes through a first end portion of the actuator mechanism. Another permament magnet mechanism defines a second magnetic flux path which passes through a second end portion of the actuator mechanism. A drive coil defines a third magnetic flux path passing through a third central portion of the actuator mechanism. A drive coil selectively adds magnetic flux to and subtracts magnetic flux from magnetic flux flowing in the first and second magnetic flux path.

Evolution of magnetic flux ropes associated with flux transfer events and interplanetary magnetic clouds

NASA Technical Reports Server (NTRS)

Wei, C. Q.; Lee, L. C.; Wang, S.; Akasofu, S.-I.

1991-01-01

Spacecraft observations suggest that flux transfer events and interplanetary magnetic clouds may be associated with magnetic flux ropes which are magnetic flux tubes containing helical magnetic field lines. In the magnetic flux ropes, the azimuthal magnetic field is superposed on the axial field. The time evolution of a localized magnetic flux rope is studied. A two-dimensional compressible MHD simulation code with a cylindrical symmetry is developed to study the wave modes associated with the evolution of flux ropes. It is found that in the initial phase both the fast magnetosonic wave and the Alfven wave are developed in the flux rope. After this initial phase, the Alfven wave becomes the dominant wave mode for the evolution of the magnetic flux rope and the radial expansion velocity of the flux rope is found to be negligible. Numerical results further show that even for a large initial azimuthal component of the magnetic field, the propagation velocity along the axial direction of the flux rope remains the Alfven velocity. It is also found that the localized magnetic flux rope tends to evolve into two separate magnetic ropes propagating in opposite directions. The simulation results are used to study the evolution of magnetic flux ropes associated with flux transfer events observed at the earth's dayside magnetopause and magnetic clouds in the interplanetary space.

Traffic flow behavior at un-signalized intersection with crossings pedestrians

NASA Astrophysics Data System (ADS)

Khallouk, A.; Echab, H.; Ez-Zahraouy, H.; Lakouari, N.

2018-02-01

Mixed traffic flux composed of crossing pedestrians and vehicles extensively exists in cities. To study the characteristics of the interference traffic flux, we develop a pedestrian-vehicle cellular automata model to present the interaction behaviors on a simple cross road. By realizing the fundamental parameters (i.e. injecting rates α1, α2, the extracting rate β and the pedestrian arrival rate αP), simulations are carried out. The vehicular traffic flux is calculated in terms of rates. The effect of the crosswalk can be regarded as a dynamic impurity. The system phase diagrams in the (α1 ,αP) plane are built. It is found that the phase diagrams consist essentially of four phases namely Free Flow, Congested, Maximal Current and Gridlock. The value of the Maximal current phase depends on the extracting rate β, while the Gridlock phase is achieved only when the pedestrians generating rate is higher than a critical value. Furthermore, the effect of vehicles changing lane (Pch1 ,Pch2) and the location of the crosswalk XP on the dynamic characteristics of vehicles flow are investigated. It is found that traffic situation in the system is slightly enhanced if the location of the crosswalks XP is far from the intersection. However, when Pch1, Pch2 increase, the traffic becomes congested and the Gridlock phase enlarges.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chang; Deng, Na; Wang, Haimin

Adverse space-weather effects can often be traced to solar flares, the prediction of which has drawn significant research interests. The Helioseismic and Magnetic Imager (HMI) produces full-disk vector magnetograms with continuous high cadence, while flare prediction efforts utilizing this unprecedented data source are still limited. Here we report results of flare prediction using physical parameters provided by the Space-weather HMI Active Region Patches (SHARP) and related data products. We survey X-ray flares that occurred from 2010 May to 2016 December and categorize their source regions into four classes (B, C, M, and X) according to the maximum GOES magnitude ofmore » flares they generated. We then retrieve SHARP-related parameters for each selected region at the beginning of its flare date to build a database. Finally, we train a machine-learning algorithm, called random forest (RF), to predict the occurrence of a certain class of flares in a given active region within 24 hr, evaluate the classifier performance using the 10-fold cross-validation scheme, and characterize the results using standard performance metrics. Compared to previous works, our experiments indicate that using the HMI parameters and RF is a valid method for flare forecasting with fairly reasonable prediction performance. To our knowledge, this is the first time that RF has been used to make multiclass predictions of solar flares. We also find that the total unsigned quantities of vertical current, current helicity, and flux near the polarity inversion line are among the most important parameters for classifying flaring regions into different classes.« less

Magnetic flux in modeled magnetic clouds at 1 AU and some specific comparisons to associated photospheric flux

NASA Technical Reports Server (NTRS)

Lepping, R. P.; Szabo, A.; DeForest, C. E.; Thompson, B. J.

1997-01-01

In order to better understand the solar origins of magnetic clouds, statistical distributions of the estimated axial magnetic flux of 30 magnetic clouds at 1 AU, separated according to their occurrence during the solar cycle, were obtained and a comparison was made of the magnetic flux of a magnetic cloud to the aggregate flux of apparently associated photospheric magnetic flux tubes, for some specific cases. The 30 magnetic clouds comprise 12 cases from WIND, and the remainder from IMP-8, earlier IMPs, the International Sun-Earth Explorer (ISEE) 3 and HELIOS. The total magnetic flux along the cloud axis was estimated using a constant alpha, cylindrical, force-free flux rope model to determine cloud diameter and axial magentic field strength. The distribution of magentic fluxes for the 30 clouds is shown to be in the form of a skewed Gaussian.

Noise and Sonic Boom Impact Technology. Initial Development of an Assessment System for Aircraft Noise (ASAN). Volume 3. Technical Description

DTIC Science & Technology

1989-06-01

field width, it will be padded on the left (or right, if the left adjustment indicator has been given) to make up the field width. The padding character...is blank (space) normally, and zero if the field width was specified with a leading zero (this zero does not imply an octal field width). 25 " a...unsigned octal notation (without a leading zero ). ’x The argument is coverted to unsigned hexadecimal notation (without a leading Ox). * u The argument is

Surprise beyond prediction error

PubMed Central

Chumbley, Justin R; Burke, Christopher J; Stephan, Klaas E; Friston, Karl J; Tobler, Philippe N; Fehr, Ernst

2014-01-01

Surprise drives learning. Various neural “prediction error” signals are believed to underpin surprise-based reinforcement learning. Here, we report a surprise signal that reflects reinforcement learning but is neither un/signed reward prediction error (RPE) nor un/signed state prediction error (SPE). To exclude these alternatives, we measured surprise responses in the absence of RPE and accounted for a host of potential SPE confounds. This new surprise signal was evident in ventral striatum, primary sensory cortex, frontal poles, and amygdala. We interpret these findings via a normative model of surprise. PMID:24700400

On turbulent diffusion of magnetic fields and the loss of magnetic flux from stars

NASA Technical Reports Server (NTRS)

Vainshtein, Samuel I.; Rosner, Robert

1991-01-01

The turbulent diffusion of magnetic fields in astrophysical objects, and the processes leading to magnetic field flux loss from such objects are discussed with attention to the suppression of turbulent diffusion by back-reaction of magnetic fields on small spatial scales, and on the constraint imposed on magnetic flux loss by flux-freezing within stars. Turbulent magnetic diffusion can be suppressed even for very weak large-scale magnetic fields, so that 'standard' turbulent diffusion is incapable of significant magnetic flux destruction within a star. Finally, magnetic flux loss via winds is shown to be generally ineffective, no matter what the value of the effective magnetic Reynolds number is.

A novel high temperature superconducting magnetic flux pump for MRI magnets

NASA Astrophysics Data System (ADS)

Bai, Zhiming; Yan, Guo; Wu, Chunli; Ding, Shufang; Chen, Chuan

2010-10-01

This paper presents a kind of minitype magnetic flux pump made of high temperature superconductor. This kind of novel high temperature superconducting (HTS) flux pump has not any mechanical revolving parts or thermal switches. The excitation current of copper coils in magnetic pole system is controlled by a singlechip. The structure design and operational principle have been described. The operating performance of the new model magnetic flux pump has been preliminarily tested. The experiments show that the maximum pumping current is approximately 200 A for Bi2223 flux pump and 80 A for MgB 2 flux pump operating at 20 K. By comparison, it is discovered that the operating temperature range is wider, the ripple is smaller and the pumping frequency is higher in Bi2223 flux pump than those in MgB 2 flux pump. These results indicate that the newly developed Bi2223 magnetic flux pump may efficiently compensate the magnetic field decay in HTS magnet and make the magnet operate in persistent current mode, this point is significant to the magnetic resonance imaging (MRI) magnets. This new flux pump is under construction presently. It is expected that the Bi2223 flux pump would be applied to the superconducting MRI magnets by further optimizing structure and improving working process.

Magnetic-flux pump

NASA Technical Reports Server (NTRS)

Hildebrandt, A. F.; Elleman, D. D.; Whitmore, F. C. (Inventor)

1966-01-01

A magnetic flux pump is described for increasing the intensity of a magnetic field by transferring flux from one location to the magnetic field. The device includes a pair of communicating cavities formed in a block of superconducting material, and a piston for displacing the trapped magnetic flux into the secondary cavity producing a field having an intense flux density.

Permanent magnet flux-biased magnetic actuator with flux feedback

NASA Technical Reports Server (NTRS)

Groom, Nelson J. (Inventor)

1991-01-01

The invention is a permanent magnet flux-biased magnetic actuator with flux feedback for adjustably suspending an element on a single axis. The magnetic actuator includes a pair of opposing electromagnets and provides bi-directional forces along the single axis to the suspended element. Permanent magnets in flux feedback loops from the opposing electromagnets establish a reference permanent magnet flux-bias to linearize the force characteristics of the electromagnets to extend the linear range of the actuator without the need for continuous bias currents in the electromagnets.

Modification of Turbulence Structures in a Channel Flow by Uniform Magnetic Fluxes

NASA Astrophysics Data System (ADS)

Lee, D.; Choi, H.; Kim, J.

1997-11-01

Effects of electromagnetic forcing on the near-wall turbulence are investigated by applying a uniform magnetic flux in a turbulent channel flow in the streamwise and spanwise directions, respectively. The base flow is a fully developed turbulent channel flow and the direct numerical simulation technique is used. The electromagnetic force induced from the magnetic fluxes reduces the intensity of the wall-layer structures and thus drag is significantly reduced. The wall-normal and spanwise velocity fluctuations and the Reynolds shear stress decrease with the increased magnetic flux in both directions. The streamwise velocity fluctuations increase with the streamwise magnetic flux, whereas they decrease with the spanwise magnetic flux. It is also shown that the spanwise magnetic flux is much more effective than the streamwise magnetic flux in reducing the skin-friction drag. Instantaneous Lorentz force vectors show that the flow motions by the near-wall vortices are directly inhibited by the spanwise magnetic flux, while they are less effectively inhibited by the streamwise magnetic flux. Other turbulence statistics that reveal the effects of the applied magnetic forcing will be presented. ^* Supported by KOSEF Contract No. 965-1008-003-2 and ONR Grant No. N00014-95-1-0352.

Superconductor magnetic reading and writing heads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, F.S.; Dugas, M.P.

1990-11-20

This paper describes a head for interfacing with a magnetic recording media. It comprises: a member of magnetic material forming at least a portion of a magnetic flux circuit ending with a pole face surface in interfacing relation to the media for establishing a main pole in proximity to the media in the magnetic flux circuit, magnetically responsive means in magnetically coupled relation to the magnetic flux circuit, means encasing at least a portion of the external surfaces of the member with superconductive material except for the media interfacing portion of the pole face surface. The encasing means including superconductingmore » material substantially surrounding the magnetic flux circuit in proximity to the pole face surface, and means establishing an environment for the superconductive material at a temperature for maintaining the superconductive material in its superconductive state, whereby magnetic flux in the magnetic flux circuit associated with the encasing means is concentrated within the magnetic flux circuit while placement of the pole face surface in proximity to the recording media permits sensitive magnetic flux controlled information exchanges between the media and the head.« less

Magnetic flux concentration and zonal flows in magnetorotational instability turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xue-Ning; Stone, James M., E-mail: xbai@cfa.harvard.edu

2014-11-20

Accretion disks are likely threaded by external vertical magnetic flux, which enhances the level of turbulence via the magnetorotational instability (MRI). Using shearing-box simulations, we find that such external magnetic flux also strongly enhances the amplitude of banded radial density variations known as zonal flows. Moreover, we report that vertical magnetic flux is strongly concentrated toward low-density regions of the zonal flow. Mean vertical magnetic field can be more than doubled in low-density regions, and reduced to nearly zero in high-density regions in some cases. In ideal MHD, the scale on which magnetic flux concentrates can reach a few diskmore » scale heights. In the non-ideal MHD regime with strong ambipolar diffusion, magnetic flux is concentrated into thin axisymmetric shells at some enhanced level, whose size is typically less than half a scale height. We show that magnetic flux concentration is closely related to the fact that the turbulent diffusivity of the MRI turbulence is anisotropic. In addition to a conventional Ohmic-like turbulent resistivity, we find that there is a correlation between the vertical velocity and horizontal magnetic field fluctuations that produces a mean electric field that acts to anti-diffuse the vertical magnetic flux. The anisotropic turbulent diffusivity has analogies to the Hall effect, and may have important implications for magnetic flux transport in accretion disks. The physical origin of magnetic flux concentration may be related to the development of channel flows followed by magnetic reconnection, which acts to decrease the mass-to-flux ratio in localized regions. The association of enhanced zonal flows with magnetic flux concentration may lead to global pressure bumps in protoplanetary disks that helps trap dust particles and facilitates planet formation.« less

Squeezing of magnetic flux in nanorings.

PubMed

Dajka, J; Ptok, A; Luczka, J

2012-12-12

We study superconducting and non-superconducting nanorings and look for non-classical features of magnetic flux passing through nanorings. We show that the magnetic flux can exhibit purely quantum properties in some peculiar states with quadrature squeezing. We identify a subset of Gazeau-Klauder states in which the magnetic flux can be squeezed and, within tailored parameter regimes, quantum fluctuations of the magnetic flux can be maximally reduced.

Magnetic Flux Density of Different Types of New Generation Magnetic Attachment Systems.

PubMed

Akin, Hakan

2015-07-01

The purpose of this study was to analyze the static magnetic flux density of different types of new generation laser-welded magnetic attachments in the single position and the attractive position and to determine the effect of different corrosive environments on magnetic flux density. Magnetic flux densities of four magnetic attachment systems (Hyper slim, Hicorex slim, Dyna, and Steco) were measured with a gaussmeter. Then magnetic attachment systems were immersed in two different media, namely 1% lactic acid solution (pH 2.3), and 0.9% NaCl solution (pH 7.3). Magnetic flux densities of the attachment systems were measured with a gaussmeter after immersion to compare with measurements before immersion (α = 0.05). The data were statistically evaluated with one-way ANOVA, paired-samples t-test, and post hoc Tukey-Kramer multiple comparisons tests (α = 0.05). The highest magnetic flux density was found in Dyna magnets for both single and attractive positions. In addition, after the magnets were in the corrosive environments for 2 weeks, they had a significant decrease in magnetic flux density (p < 0.05). No significant differences were found between corrosive environments (p > 0.05). The leakage flux of all the magnetic attachments did not exceed the WHO's guideline of 40 mT. The magnets exhibited a significant decrease in magnetic flux density after aging in corrosive environments including lactic acid and NaCl. © 2014 by the American College of Prosthodontists.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, John R.

1997-01-01

A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, John R.

1996-01-01

A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

Physics of magnetic flux ropes

NASA Astrophysics Data System (ADS)

Russell, C. T.; Priest, E. R.; Lee, L. C.

The present work encompasses papers on the structure, waves, and instabilities of magnetic flux ropes (MFRs), photospheric flux tubes (PFTs), the structure and heating of coronal loops, solar prominences, coronal mass ejections and magnetic clouds, flux ropes in planetary ionospheres, the magnetopause, magnetospheric field-aligned currents and flux tubes, and the magnetotail. Attention is given to the equilibrium of MFRs, resistive instability, magnetic reconnection and turbulence in current sheets, dynamical effects and energy transport in intense flux tubes, waves in solar PFTs, twisted flux ropes in the solar corona, an electrodynamical model of solar flares, filament cooling and condensation in a sheared magnetic field, the magnetopause, the generation of twisted MFRs during magnetic reconnection, ionospheric flux ropes above the South Pole, substorms and MFR structures, evidence for flux ropes in the earth magnetotail, and MFRs in 3D MHD simulations.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, J.R.

1997-08-05

A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, J.R.

1996-10-08

A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

THE TOPOLOGY OF CANONICAL FLUX TUBES IN FLARED JET GEOMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavine, Eric Sander; You, Setthivoine, E-mail: Slavine2@uw.edu, E-mail: syou@aa.washington.edu

2017-01-20

Magnetized plasma jets are generally modeled as magnetic flux tubes filled with flowing plasma governed by magnetohydrodynamics (MHD). We outline here a more fundamental approach based on flux tubes of canonical vorticity, where canonical vorticity is defined as the circulation of the species’ canonical momentum. This approach extends the concept of magnetic flux tube evolution to include the effects of finite particle momentum and enables visualization of the topology of plasma jets in regimes beyond MHD. A flared, current-carrying magnetic flux tube in an ion-electron plasma with finite ion momentum is thus equivalent to either a pair of electron andmore » ion flow flux tubes, a pair of electron and ion canonical momentum flux tubes, or a pair of electron and ion canonical vorticity flux tubes. We examine the morphology of all these flux tubes for increasing electrical currents, different radial current profiles, different electron Mach numbers, and a fixed, flared, axisymmetric magnetic geometry. Calculations of gauge-invariant relative canonical helicities track the evolution of magnetic, cross, and kinetic helicities in the system, and show that ion flow fields can unwind to compensate for an increasing magnetic twist. The results demonstrate that including a species’ finite momentum can result in a very long collimated canonical vorticity flux tube even if the magnetic flux tube is flared. With finite momentum, particle density gradients must be normal to canonical vorticities, not to magnetic fields, so observations of collimated astrophysical jets could be images of canonical vorticity flux tubes instead of magnetic flux tubes.« less

Force sensor using changes in magnetic flux

NASA Technical Reports Server (NTRS)

Pickens, Herman L. (Inventor); Richard, James A. (Inventor)

2012-01-01

A force sensor includes a magnetostrictive material and a magnetic field generator positioned in proximity thereto. A magnetic field is induced in and surrounding the magnetostrictive material such that lines of magnetic flux pass through the magnetostrictive material. A sensor positioned in the vicinity of the magnetostrictive material measures changes in one of flux angle and flux density when the magnetostrictive material experiences an applied force that is aligned with the lines of magnetic flux.

Self-organization in magnetic flux ropes

NASA Astrophysics Data System (ADS)

Lukin, Vyacheslav S.

2014-06-01

This cross-disciplinary special issue on 'Self-organization in magnetic flux ropes' follows in the footsteps of another collection of manuscripts dedicated to the subject of magnetic flux ropes, a volume on 'Physics of magnetic flux ropes' published in the American Geophysical Union's Geophysical Monograph Series in 1990 [1]. Twenty-four years later, this special issue, composed of invited original contributions highlighting ongoing research on the physics of magnetic flux ropes in astrophysical, space and laboratory plasmas, can be considered an update on our state of understanding of this fundamental constituent of any magnetized plasma. Furthermore, by inviting contributions from research groups focused on the study of the origins and properties of magnetic flux ropes in a variety of different environments, we have attempted to underline both the diversity of and the commonalities among magnetic flux ropes throughout the solar system and, indeed, the universe. So, what is a magnetic flux rope? The answer will undoubtedly depend on whom you ask. A flux rope can be as narrow as a few Larmor radii and as wide as the Sun (see, e.g., the contributions by Heli Hietala et al and by Angelous Vourlidas). As described below by Ward Manchester IV et al , they can stretch from the Sun to the Earth in the form of interplanetary coronal mass ejections. Or, as in the Swarthmore Spheromak Experiment described by David Schaffner et al , they can fit into a meter-long laboratory device tended by college students. They can be helical and line-tied (see, e.g., Walter Gekelman et al or J Sears et al ), or toroidal and periodic (see, e.g., John O'Bryan et al or Philippa Browning et al ). They can form in the low plasma beta environment of the solar corona (Tibor Török et al ), the order unity beta plasmas of the solar wind (Stefan Eriksson et al ) and the plasma pressure dominated stellar convection zones (Nicholas Nelson and Mark Miesch). In this special issue, Setthivoine You describes how canonical helicity can determine the result of reconnection and merging of multiple magnetic flux ropes, John Finn et al focus on diagnosing flux rope reconnection using quasi-separatrix layers, and Stefano Markidis et al investigate how a single flux rope can become unstable and begin to fall apart. With these many examples of different magnetized plasma structures, which can all be called magnetic flux ropes, the question still stands: just what is it that makes a volume of magnetized plasma a magnetic flux rope? There may not be a strict definition of a magnetic flux rope that everyone can agree on. Nonetheless, the ingredient common to all magnetic flux ropes is that the magnetic field lines that thread nearby plasma elements at one location along the flux rope must wind around and not diverge away from each other over a sufficiently long distance to look like a piece of an ordinary rope. In a way, it is similar to turbulence—you know it when you see it. The figures and illustrations included in this special issue provide plenty of examples of observed, measured, modeled and imagined magnetic flux ropes for you, the reader, to develop an appreciation of what different members of our research community mean by a magnetic flux rope. If you have never studied magnetic flux ropes, we hope that this special issue inspires you to look into their many mysteries. If magnetic flux ropes are already an integral part of your research, we hope the diversity of perspectives presented herein refresh your interest in the underlying plasma physics of whichever kind of magnetic flux rope you happen to be working with. References [1] Russell C T, Priest E R and Lee L-C 1990 Physics of Magnetic Flux Ropes AGU Geophysical Monograph Series vol 58 (Washington, DC: American Geophysical Union)

Correlations Between Magnetic Flux and Levitation Force of HTS Bulk Above a Permanent Magnet Guideway

NASA Astrophysics Data System (ADS)

Huang, Huan; Zheng, Jun; Zheng, Botian; Qian, Nan; Li, Haitao; Li, Jipeng; Deng, Zigang

2017-10-01

In order to clarify the correlations between magnetic flux and levitation force of the high-temperature superconducting (HTS) bulk, we measured the magnetic flux density on bottom and top surfaces of a bulk superconductor while vertically moving above a permanent magnet guideway (PMG). The levitation force of the bulk superconductor was measured simultaneously. In this study, the HTS bulk was moved down and up for three times between field-cooling position and working position above the PMG, followed by a relaxation measurement of 300 s at the minimum height position. During the whole processes, the magnetic flux density and levitation force of the bulk superconductor were recorded and collected by a multipoint magnetic field measurement platform and a self-developed maglev measurement system, respectively. The magnetic flux density on the bottom surface reflected the induced field in the superconductor bulk, while on the top, it reveals the penetrated magnetic flux. The results show that the magnetic flux density and levitation force of the bulk superconductor are in direct correlation from the viewpoint of inner supercurrent. In general, this work is instructive for understanding the connection of the magnetic flux density, the inner current density and the levitation behavior of HTS bulk employed in a maglev system. Meanwhile, this magnetic flux density measurement method has enriched present experimental evaluation methods of maglev system.

[Factors for Degaussing of a Cochlear Implant Magnet in the MR Scanner].

PubMed

Koganezawa, Takumi; Uchiyama, Naoko; Teshigawara, Mai; Ogura, Akio

This study examined the conditions influencing degauss of the magnet using magnetic resonance imaging (MRI). Poly methyl methacrylate (PMMA) was used to fix the measurement magnets to the MRI bed at angles from 0° to 180° for the magnetic flux vector of static magnetic field. The PMMA was moved in the MRI magnetic field. Magnetic flux density was measured before and after bed movement, and the rate of degauss was calculated. The contents examined are as follows: (1) the angle of the magnetic flux vector of the measurement magnets for the magnetic flux vector of the static magnetic field, (2) the number of movements, (3) moving velocity, and (4) the movement on the spatial gradient of magnetic field. Mann-Whitney U test was used for statistical analysis of the data. In conclusion, the effect of the angle of the magnetic flux vector of the implant magnet was high under the conditions of degauss in this study. Therefore, during the MRI examination of a patient with a cochlear implant magnet, the operators identified the directions of the magnetic flux vector and static magnetic field of the implant magnet.

Topology of magnetic flux ropes and formation of fossil flux transfer events and boundary layer plasmas

NASA Technical Reports Server (NTRS)

Lee, L. C.; Ma, Z. W.; Fu, Z. F.; Otto, A.

1993-01-01

A mechanism for the formation of fossil flux transfer events and the low-level boundary layer within the framework of multiple X-line reconnection is proposed. Attention is given to conditions for which the bulk of magnetic flux in a flux rope of finite extent has a simple magnetic topology, where the four possible connections of magnetic field lines are: IMF to MSP, MSP to IMF, IMF to IMF, and MSP to MSP. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnetic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. This process is discussed as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low-latitude boundary layer.

DO THE LEGS OF MAGNETIC CLOUDS CONTAIN TWISTED FLUX-ROPE MAGNETIC FIELDS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Owens, M. J.

2016-02-20

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux ropemore » would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC “legs,” which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.« less

Siphon flows in isolated magnetic flux tubes. IV - Critical flows with standing tube shocks

NASA Technical Reports Server (NTRS)

Thomas, John H.; Montesinos, Benjamin

1991-01-01

Critical siphon flows in arched, isolated magnetic flux tubes are studied within the thin flux tube approximation, with a view toward applications to intense magnetic flux concentrations in the solar photosphere. The results of calculations of the strength and position of the standing tube shock in the supercritical downstream branch of a critical siphon flow are presented, as are calculations of the flow variables all along the flux tube and the equilibrium path of the flux tube in the surrounding atmosphere. It is suggested that arched magnetic flux tubes, with magnetic field strength increased by a siphon flow, may be associated with some of the intense, discrete magnetic elements observed in the solar photosphere.

[Measurements of the flux densities of static magnetic fields generated by two types of dental magnetic attachments and their retentive forces].

PubMed

Xu, Chun; Chao, Yong-lie; Du, Li; Yang, Ling

2004-05-01

To measure and analyze the flux densities of static magnetic fields generated by two types of commonly used dental magnetic attachments and their retentive forces, and to provide guidance for the clinical application of magnetic attachments. A digital Gaussmeter was used to measure the flux densities of static magnetic fields generated by two types of magnetic attachments, under four circumstances: open-field circuit; closed-field circuit; keeper and magnet slid laterally for a certain distance; and existence of air gap between keeper and magnet. The retentive forces of the magnetic attachments in standard closed-field circuit, with the keeper and magnet sliding laterally for a certain distance or with a certain air gap between keeper and magnet were measured by a tensile testing machine. There were flux leakages under both the open-field circuit and closed-field circuit of the two types of magnetic attachments. The flux densities on the surfaces of MAGNEDISC 800 (MD800) and MAGFIT EX600W (EX600) magnetic attachments under open-field circuit were 275.0 mT and 147.0 mT respectively. The flux leakages under closed-field circuit were smaller than those under open-field circuit. The respective flux densities on the surfaces of MD800 and EX600 magnetic attachments decreased to 11.4 mT and 4.5 mT under closed-field circuit. The flux density around the magnetic attachment decreased as the distance from the surface of the attachment increased. When keeper and magnet slid laterally for a certain distance or when air gap existed between keeper and magnet, the flux leakage increased in comparison with that under closed-field circuit. Under the standard closed-field circuit, the two types of magnetic attachments achieved the largest retentive forces. The retentive forces of MD800 and EX600 magnetic attachments under the standard closed-field circuit were 6.20 N and 4.80 N respectively. The retentive forces decreased with the sliding distance or with the increase of air gap between keeper and magnet. The magnetic attachments have flux leakages. When they are used in patients' oral cavities, if keeper and magnet are not attached accurately, the flux leakage will increase, and at the same time the retentive force will decrease. Therefore the keeper and magnet should be attached accurately in clinical application.

Forced three-dimensional magnetic reconnection due to linkage of magnetic flux tubes

NASA Technical Reports Server (NTRS)

Otto, A.

1995-01-01

During periods of southward interplanetary magnetic field (IMF) orientation the magnetic field geometry at the dayside magnetopause is susceptible to magnetic reconnection. It has been suggested that reconnection may occur in a localized manner at several patches on the magnetopause. A major problem with this picture is the interaction of magnetic flux ropes which are generated by different reconnection processes. An individual flux rope is bent elbowlike where it intersects the magnetopause and the magnetic field changes from magnetospheric to interplanetary magnetic field orientation. Multiple patches of reconnection can lead to the formation of interlinked magnetic flux tubes. Although the corresponding flux is connected to the IMF the northward and southward connected branches are hooked into each other and cannot develop independently. We have studied this problem in the framework of three-dimensional magnetohydrodynamic simulations. The results indicate that a singular current sheet forms at the interface of two interlinked flux tubes if no resistivity is present in the simulation. This current sheet is strongly tilted compared to the original current sheet. In the presence of resistivity the interaction of the two flux tubes forces a fast reconnection process which generates helically twisted closed magnetospheric flux. This linkage induced reconnection generates a boundary layer with layers of open and closed magnetospheric flux and may account for the brightening of auroral arcs poleward of the boundary between open and closed magnetic flux.

SecureQEMU: Emulation-Based Software Protection Providing Encrypted Code Execution and Page Granularity Code Signing

DTIC Science & Technology

2008-12-01

SHA256 DIGEST LENGTH) ) ; peAddSection(&sF i l e , " . S i g S t u b " , dwStubSecSize , dwStubSecSize ) ; 169 peSecure(&sF i l e , deqAddrSize...deqAuthPageAddrSize . s i z e ( ) /2) ∗ (8 + SHA256 DIGEST LENGTH) ) + 16 ; bCode [ 3 4 ] = ( ( char∗)&dwSize ) [ 0 ] ; bCode [ 3 5 ] = ( ( char∗)&dwSize ) [ 1...2) ∗ (8 + SHA256 DIGEST LENGTH... ) ) ; AES KEY aesKey ; unsigned char i v s a l t [ 1 6 ] , temp iv [ 1 6 ] ; 739 unsigned char ∗key

Pavlovian contingencies and temporal information.

PubMed

Balsam, Peter D; Fairhurst, Stephen; Gallistel, Charles R

2006-07-01

The effects of altering the contingency between the conditioned stimulus (CS) and the unconditioned stimulus (US) on the acquisition of autoshaped responding was investigated by changing the frequency of unsignaled USs during the intertrial interval. The addition of the unsignaled USs had an effect on acquisition speed comparable with that of massing trials. The effects of these manipulations can be understood in terms of their effect on the amount of information (number of bits) that the average CS conveys to the subject about the timing of the next US. The number of reinforced CSs prior to acquisition is inversely related to the information content of the CS.

The 6-31B(d) basis set and the BMC-QCISD and BMC-CCSD multicoefficient correlation methods.

PubMed

Lynch, Benjamin J; Zhao, Yan; Truhlar, Donald G

2005-03-03

Three new multicoefficient correlation methods (MCCMs) called BMC-QCISD, BMC-CCSD, and BMC-CCSD-C are optimized against 274 data that include atomization energies, electron affinities, ionization potentials, and reaction barrier heights. A new basis set called 6-31B(d) is developed and used as part of the new methods. BMC-QCISD has mean unsigned errors in calculating atomization energies per bond and barrier heights of 0.49 and 0.80 kcal/mol, respectively. BMC-CCSD has mean unsigned errors of 0.42 and 0.71 kcal/mol for the same two quantities. BMC-CCSD-C is an equally effective variant of BMC-CCSD that employs Cartesian rather than spherical harmonic basis sets. The mean unsigned error of BMC-CCSD or BMC-CCSD-C for atomization energies, barrier heights, ionization potentials, and electron affinities is 22% lower than G3SX(MP2) at an order of magnitude less cost for gradients for molecules with 9-13 atoms, and it scales better (N6 vs N,7 where N is the number of atoms) when the size of the molecule is increased.

Signal functions in delayed reinforcement

PubMed Central

Lattal, Kennon A.

1984-01-01

Three experiments were conducted with pigeons to examine the role of the signal in delay-of-reinforcement procedures. In the first, a blackout accompanying a period of nonreinforcement increased key-peck response rates maintained by immediate reinforcement. The effects of dissociating the blackout from the delay interval were examined in the second experiment. In three conditions, blackouts and unsignaled delays were negatively correlated or occurred randomly with respect to one another. A signaled delay and an unsignaled delay that omitted the blackouts were studied in two other conditions. All delay-of-reinforcement conditions generally produced response rates lower than those produced by immediate reinforcement. Signaled delays maintained higher response rates than did any of the various unsignaled-delay conditions, with or without dissociated blackouts. The effects of these latter conditions did not differ systematically from one another. The final experiment showed that response rates varied as a function of the frequency with which a blackout accompanied delay intervals. By eliminating a number of methodological difficulties present in previous delay-of-reinforcement experiments, these results suggest the importance of the signal in maintaining responding during delay-of-reinforcement procedures and, conversely, the importance of the delay interval in decreasing responding. PMID:16812387

Estimating Total Heliospheric Magnetic Flux from Single-Point in Situ Measurements

NASA Technical Reports Server (NTRS)

Owens, M. J.; Arge, C. N.; Crooker, N. U.; Schwardron, N. A.; Horbury, T. S.

2008-01-01

A fraction of the total photospheric magnetic flux opens to the heliosphere to form the interplanetary magnetic field carried by the solar wind. While this open flux is critical to our understanding of the generation and evolution of the solar magnetic field, direct measurements are generally limited to single-point measurements taken in situ by heliospheric spacecraft. An observed latitude invariance in the radial component of the magnetic field suggests that extrapolation from such single-point measurements to total heliospheric magnetic flux is possible. In this study we test this assumption using estimates of total heliospheric flux from well-separated heliospheric spacecraft and conclude that single-point measurements are indeed adequate proxies for the total heliospheric magnetic flux, though care must be taken when comparing flux estimates from data collected at different heliocentric distances.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raminosoa, Tsarafidy; Alexander, James Pellegrino; EL-Refaie, Ayman Mohamed Fawzi

A permanent magnet electrical machine includes a stator having conductive windings wound thereon and one or more permanent magnets embedded in the stator. A magnetic keeper element is positioned on the stator so as to form a magnetic flux path with the permanent magnets, with the magnetic keeper element closing the magnetic flux path of the permanent magnets by providing a low reluctance flux path to magnetic flux generated by the permanent magnets. A vacuum pressure impregnation (VPI) process is performed on the stator to increase a thermal conductivity of the windings, with the VPI process including a curing stepmore » that is performed at a selected temperature. The magnetic keeper element sets an operating point of the permanent magnets to an internal flux density level above a demagnetization threshold associated with the selected temperature at which the curing step is performed.« less

Three-dimensional magnetohydrodynamics of the emerging magnetic flux in the solar atmosphere

NASA Technical Reports Server (NTRS)

Matsumoto, R.; Tajima, T.; Shibata, K.; Kaisig, M.

1993-01-01

The nonlinear evolution of an emerging magnetic flux tube or sheet in the solar atmosphere is studied through 3D MHD simulations. In the initial state, a horizontal magnetic flux sheet or tube is assumed to be embedded at the bottom of MHD two isothermal gas layers, which approximate the solar photosphere/chromosphere and the corona. The magnetic flux sheet or tube is unstable against the undular mode of the magnetic buoyancy instability. The magnetic loop rises due to the linear and then later nonlinear instabilities caused by the buoyancy enhanced by precipitating the gas along magnetic field lines. We find by 3D simulation that during the ascendance of loops the bundle of flux tubes or even the flux sheet develops into dense gas filaments pinched between magnetic loops. The interchange modes help produce a fine fiber flux structure perpendicular to the magnetic field direction in the linear stage, while the undular modes determine the overall buoyant loop structure. The expansion of such a bundle of magnetic loops follows the self-similar behavior observed in 2D cases studied earlier. Our study finds the threshold flux for arch filament system (AFS) formation to be about 0.3 x 10 exp 20 Mx.

Magnetic Force Switches for Magnetic Fluid Micromixing

NASA Astrophysics Data System (ADS)

Wei, Zung-Hang; Lee, Chiun-Peng; Lai, Mei-Feng

2010-01-01

A magnetic fluid micromixer with energy-saving magnetic force switches that can manipulate the magnetic fluid flow is proposed. The micromixer of high mixing efficiency uses single-domain micro magnets that have strong magnetic anisotropy to produce the magnetic force for the mixing. By altering the magnetization directions of the magnets that have different aspect ratios and coercivities, open and closed magnetic fluxes can be produced around each magnet cluster. For open magnetic flux, the mixing efficiency is numerically found to increase with the saturation magnetization of the magnets. On the contrary, the magnet clusters barely affects the mixing efficiency in the case of closed magnetic flux. Due to the different magnetic forces produced in open and closed magnetic fluxes, the magnetic fluid mixing can be switched on and off.

The magnetic non-equilibrium of buoyant flux tubes in the solar corona

NASA Technical Reports Server (NTRS)

Browning, P. K.; Priest, E. R.

1984-01-01

The magnetic field in the convection zone and photosphere of the sun exists mostly as concentrated tubes of magnetic flux. It is, therefore, necessary to study the basic properties of magnetic flux tubes to obtain a basis for understanding the behavior of the sun's magnetic field. The present investigation is concerned with the global equilibrium shape of a flux tube in the stratified solar atmosphere. A fundamental property of isolated flux tubes is magnetic buoyancy. Attention is given to flux tubes with external field, and twisted flux tubes. It is shown that the analysis of Parker (1975, 1979) and Spruit (1981) for calculating the equilibrium of a slender flux tube in a stratified atmosphere may be extended to more general situations. The slender tube approximation provides a method of solving the problem of modeling the overall curvature of flux tubes. It is found that for a twisted flux tube, there can be two possible equilibrium values of the height.

The photospheric magnetic flux budget

NASA Technical Reports Server (NTRS)

Schrijver, C. J.; Harvey, K. L.

1994-01-01

The ensemble of bipolar regions and the magnetic network both contain a substantial and strongly variable part of the photospheric magnetic flux at any phase in the solar cycle. The time-dependent distribution of the magnetic flux over and within these components reflects the action of the dynamo operating in the solar interior. We perform a quantitative comparison of the flux emerging in the ensemble of magnetic bipoles with the observed flux content of the solar photosphere. We discuss the photospheric flux budget in terms of flux appearance and disappearance, and argue that a nonlinear dependence exists between the flux present in the photosphere and the rate of flux appearance and disappearance. In this context, we discuss the problem of making quantitative statements about dynamos in cool stars other than the Sun.

Effect of an External Magnetic Flux on Antitumor Antibiotic Neocarzinostatin Yield by Streptomyces carzinostaticus var. F-41

NASA Astrophysics Data System (ADS)

Kudo, Kozo; Yoshida, Yuko; Yoshimura, Noboru; Ishida, Nakao

1993-11-01

The yield of the antitumor antibiotic neocarzinostatin (NCS), produced by Streptomyces carzinostaticus var. F-41, was sensitive to an external magnetic flux. When this strain was cultivated at 28°C in a NCS-producing medium under various magnetic flux densities, good NCS yield was observed at below 250 G magnetic flux density during the exponential growth phase as compared with that obtained in the same medium without magnetic flux, but was not observed at more than 500 G. However, no definite effect on the physiological characteristics and carbohydrate utilization of this strain, and primary physicochemical properties of NCS from magnetic flux could be detected.

Design and analysis of a 3D-flux flux-switching permanent magnet machine with SMC cores and ferrite magnets

NASA Astrophysics Data System (ADS)

Liu, Chengcheng; Wang, Youhua; Lei, Gang; Guo, Youguang; Zhu, Jianguo

2017-05-01

Since permanent magnets (PM) are stacked between the adjacent stator teeth and there are no windings or PMs on the rotor, flux-switching permanent magnet machine (FSPMM) owns the merits of good flux concentrating and robust rotor structure. Compared with the traditional PM machines, FSPMM can provide higher torque density and better thermal dissipation ability. Combined with the soft magnetic composite (SMC) material and ferrite magnets, this paper proposes a new 3D-flux FSPMM (3DFFSPMM). The topology and operation principle are introduced. It can be found that the designed new 3DFFSPMM has many merits over than the traditional FSPMM for it can utilize the advantages of SMC material. Moreover, the PM flux of this new motor can be regulated by using the mechanical method. 3D finite element method (FEM) is used to calculate the magnetic field and parameters of the motor, such as flux density, inductance, PM flux linkage and efficiency map. The demagnetization analysis of the ferrite magnet is also addressed to ensure the safety operation of the proposed motor.

Quantum transport in coupled resonators enclosed synthetic magnetic flux

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, L., E-mail: jinliang@nankai.edu.cn

Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmissionmore » zeros in an interferometer with two equal arms. -- Highlights: •The light transport is investigated through ring array of coupled resonators enclosed synthetic magnetic field. •Aharonov–Bohm ring interferometer of arbitrary configuration is investigated. •The half-integer magnetic flux quantum leads to destructive interference and transmission zeros for two-arm at equal length. •Complete transmission is available via tuning synthetic magnetic flux.« less

On Magnetic Flux Trapping by Surface Superconductivity

NASA Astrophysics Data System (ADS)

Podolyak, E. R.

2018-03-01

The magnetic flux trapping by surface superconductivity is considered. The stability of the state localized at the cylindrical sample surface upon a change in the external magnetic field is tested. It is shown that as the magnetic field decreases, the sample acquires a positive magnetic moment due to magnetic flux trapping; i.e., the magnetization curve of surface superconductivity is "paramagnetic" by nature.

Levitation in the field of a nonsuperconducting coil with magnetic flux stabilization

NASA Astrophysics Data System (ADS)

Koshurnikov, E. K.

2013-09-01

A method providing the "frozen flux" conditions in a nonsuperconducting coil is suggested and demonstrated with a model. The feasibility of permanent magnet stable levitation in the field of the coil with magnetic flux stabilization and mean current control is shown. The method allows researchers to exploit permanent magnet-superconducting body interaction in physical devices, for example, to reproduce, using nonsuperconducting coils, the frozen magnetic flux conditions required for the stable levitation of the magnet over a superconducting body.

A magnetoelectric flux gate: new approach for weak DC magnetic field detection.

PubMed

Chu, Zhaoqiang; Shi, Huaduo; PourhosseiniAsl, Mohammad Javad; Wu, Jingen; Shi, Weiliang; Gao, Xiangyu; Yuan, Xiaoting; Dong, Shuxiang

2017-08-17

The magnetic flux gate sensors based on Faraday's Law of Induction are widely used for DC or extremely low frequency magnetic field detection. Recently, as the fast development of multiferroics and magnetoelectric (ME) composite materials, a new technology based on ME coupling effect is emerging for potential devices application. Here, we report a magnetoelectric flux gate sensor (MEFGS) for weak DC magnetic field detection for the first time, which works on a similar magnetic flux gate principle, but based on ME coupling effect. The proposed MEFGS has a shuttle-shaped configuration made of amorphous FeBSi alloy (Metglas) serving as both magnetic and magnetostrictive cores for producing a closed-loop high-frequency magnetic flux and also a longitudinal vibration, and one pair of embedded piezoelectric PMN-PT fibers ([011]-oriented Pb(Mg,Nb)O 3 -PbTiO 3 single crystal) serving as ME flux gate in a differential mode for detecting magnetic anomaly. In this way, the relative change in output signal of the MEFGS under an applied DC magnetic anomaly of 1 nT was greatly enhanced by a factor of 4 to 5 in comparison with the previous reports. The proposed ME flux gate shows a great potential for magnetic anomaly detections, such as magnetic navigation, magnetic based medical diagnosis, etc.

Magnetic flux conservation in an imploding plasma.

PubMed

García-Rubio, F; Sanz, J; Betti, R

2018-01-01

The theory of magnetic flux conservation is developed for a subsonic plasma implosion and used to describe the magnetic flux degradation in the MagLIF concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)10.1063/1.3333505]. Depending on the initial magnetic Lewis and Péclet numbers and the electron Hall parameter, the implosion falls into either a superdiffusive regime in which the magnetization decreases or a magnetized regime in which the magnetization increases. Scaling laws for magnetic field, temperature, and magnetic flux losses in the hot spot of radius R are obtained for both regimes. The Nernst velocity convects the magnetic field outwards, pushing it against the liner and enhancing the magnetic field diffusion, thereby reducing the magnetic field compression and degrading the implosion performance. However, in the magnetized regime, the core of the hot spot becomes magnetically insulated and undergoes an ideal adiabatic compression (T∼R^{-4/3} compared to T∼R^{-2/3} without magnetic field), while the detrimental Nernst term is confined to the outer part of the hot spot. Its effect is drastically reduced, improving the magnetic flux conservation.

Magnetic flux conservation in an imploding plasma

NASA Astrophysics Data System (ADS)

García-Rubio, F.; Sanz, J.; Betti, R.

2018-01-01

The theory of magnetic flux conservation is developed for a subsonic plasma implosion and used to describe the magnetic flux degradation in the MagLIF concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010), 10.1063/1.3333505]. Depending on the initial magnetic Lewis and Péclet numbers and the electron Hall parameter, the implosion falls into either a superdiffusive regime in which the magnetization decreases or a magnetized regime in which the magnetization increases. Scaling laws for magnetic field, temperature, and magnetic flux losses in the hot spot of radius R are obtained for both regimes. The Nernst velocity convects the magnetic field outwards, pushing it against the liner and enhancing the magnetic field diffusion, thereby reducing the magnetic field compression and degrading the implosion performance. However, in the magnetized regime, the core of the hot spot becomes magnetically insulated and undergoes an ideal adiabatic compression (T ˜R-4 /3 compared to T ˜R-2 /3 without magnetic field), while the detrimental Nernst term is confined to the outer part of the hot spot. Its effect is drastically reduced, improving the magnetic flux conservation.

Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

NASA Technical Reports Server (NTRS)

Hesse, Michael; Birn, Joachim; Pulkkinen, Tuija

1996-01-01

The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

Hall Effect–Mediated Magnetic Flux Transport in Protoplanetary Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xue-Ning; Stone, James M.

2017-02-10

The global evolution of protoplanetary disks (PPDs) has recently been shown to be largely controlled by the amount of poloidal magnetic flux threading the disk. The amount of magnetic flux must also coevolve with the disk, as a result of magnetic flux transport, a process that is poorly understood. In weakly ionized gas as in PPDs, magnetic flux is largely frozen in the electron fluid, except when resistivity is large. When the disk is largely laminar, we show that the relative drift between the electrons and ions (the Hall drift), and the ions and neutral fluids (ambipolar drift) can playmore » a dominant role on the transport of magnetic flux. Using two-dimensional simulations that incorporate the Hall effect and ambipolar diffusion (AD) with prescribed diffusivities, we show that when large-scale poloidal field is aligned with disk rotation, the Hall effect rapidly drags magnetic flux inward at the midplane region, while it slowly pushes flux outward above/below the midplane. This leads to a highly radially elongated field configuration as a global manifestation of the Hall-shear instability. This field configuration further promotes rapid outward flux transport by AD at the midplane, leading to instability saturation. In quasi-steady state, magnetic flux is transported outward at approximately the same rate at all heights, and the rate is comparable to the Hall-free case. For anti-aligned field polarity, the Hall effect consistently transports magnetic flux outward, leading to a largely vertical field configuration in the midplane region. The field lines in the upper layer first bend radially inward and then outward to launch a disk wind. Overall, the net rate of outward flux transport is about twice as fast as that of the aligned case. In addition, the rate of flux transport increases with increasing disk magnetization. The absolute rate of transport is sensitive to disk microphysics, which remains to be explored in future studies.« less

A Sun-to-Earth Analysis of Magnetic Helicity of the 2013 March 17–18 Interplanetary Coronal Mass Ejection

NASA Astrophysics Data System (ADS)

Pal, Sanchita; Gopalswamy, Nat; Nandy, Dibyendu; Akiyama, Sachiko; Yashiro, Seiji; Makela, Pertti; Xie, Hong

2017-12-01

We compare the magnetic helicity in the 2013 March 17–18 interplanetary coronal mass ejection (ICME) flux rope at 1 au and in its solar counterpart. The progenitor coronal mass ejection (CME) erupted on 2013 March 15 from NOAA active region 11692 and is associated with an M1.1 flare. We derive the source region reconnection flux using the post-eruption arcade (PEA) method that uses the photospheric magnetogram and the area under the PEA. The geometrical properties of the near-Sun flux rope is obtained by forward-modeling of white-light CME observations. Combining the geometrical properties and the reconnection flux, we extract the magnetic properties of the CME flux rope. We derive the magnetic helicity of the flux rope using its magnetic and geometric properties obtained near the Sun and at 1 au. We use a constant-α force-free cylindrical flux rope model fit to the in situ observations in order to derive the magnetic and geometric information of the 1 au ICME. We find a good correspondence in both amplitude and sign of the helicity between the ICME and the CME, assuming a semi-circular (half torus) ICME flux rope with a length of π au. We find that about 83% of the total flux rope helicity at 1 au is injected by the magnetic reconnection in the low corona. We discuss the effect of assuming flux rope length in the derived value of the magnetic helicity. This study connecting the helicity of magnetic flux ropes through the Sun–Earth system has important implications for the origin of helicity in the interplanetary medium and the topology of ICME flux ropes at 1 au and hence their space weather consequences.

Are Polar Field Magnetic Flux Concentrations Responsible for Missing Interplanetary Flux?

NASA Astrophysics Data System (ADS)

Linker, Jon A.; Downs, C.; Mikic, Z.; Riley, P.; Henney, C. J.; Arge, C. N.

2012-05-01

Magnetohydrodynamic (MHD) simulations are now routinely used to produce models of the solar corona and inner heliosphere for specific time periods. These models typically use magnetic maps of the photospheric magnetic field built up over a solar rotation, available from a number of ground-based and space-based solar observatories. The line-of-sight field at the Sun's poles is poorly observed, and the polar fields in these maps are filled with a variety of interpolation/extrapolation techniques. These models have been found to frequently underestimate the interplanetary magnetic flux (Riley et al., 2012, in press, Stevens et al., 2012, in press) near the minimum part of the cycle unless mitigating correction factors are applied. Hinode SOT observations indicate that strong concentrations of magnetic flux may be present at the poles (Tsuneta et al. 2008). The ADAPT flux evolution model (Arge et al. 2010) also predicts the appearance of such concentrations. In this paper, we explore the possibility that these flux concentrations may account for a significant amount of magnetic flux and alleviate discrepancies in interplanetary magnetic flux predictions. Research supported by AFOSR, NASA, and NSF.

Flare-CME characteristics from Sun to Earth combining observations and modeling

NASA Astrophysics Data System (ADS)

Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin; Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen; Rodriguez, Luciano

2017-04-01

We analyze the well observed flare-CME event from October 1, 2011 (SOL2011-10-01T09:18) covering the complete chain of action - from Sun to Earth - for a better understanding of the dynamic evolution of the CME and its embedded magnetic field. We study in detail the solar surface and atmosphere from SDO and ground-based instruments associated to the flare-CME and also track the CME signature offlimb from combined EUV and white-light data with STEREO. By applying 3D reconstruction techniques (GCS, total mass) to stereoscopic STEREO-SoHO coronagraph data, we track the temporal and spatial evolution of the CME in interplanetary space and derive its geometry and 3D-mass. We combine the GCS and Lundquist model results to derive the axial flux and helicity of the MC from in situ measurements (Wind). This is compared to nonlinear force-free (NLFF) model results as well as to the reconnected magnetic flux derived from the flare ribbons (flare reconnection flux) and the magnetic flux encompassed by the associated dimming (dimming flux). We find that magnetic reconnection processes were already ongoing before the start of the impulsive flare phase, adding magnetic flux to the flux rope before its final eruption. The dimming flux increases by more than 25% after the end of the flare, indicating that magnetic flux is still added to the flux rope after eruption. Hence, the derived flare reconnection flux is most probably a lower limit for estimating the magnetic flux within the flux rope. We obtain that the magnetic helicity and axial magnetic flux are reduced in interplanetary space by ˜50% and 75%, respectively, possibly indicating to an erosion process. A mass increase of 10% for the CME is observed over the distance range from about 4-20 Rs. The temporal evolution of the CME associated core dimming regions supports the scenario that fast outflows might supply additional mass to the rear part of the CME.

INVESTIGATION OF HELICITY AND ENERGY FLUX TRANSPORT IN THREE EMERGING SOLAR ACTIVE REGIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vemareddy, P., E-mail: vemareddy@iiap.res.in

We report the results of an investigation of helicity and energy flux transport from three emerging solar active regions (ARs). Using time sequence vector magnetic field observations obtained from the Helioseismic Magnetic Imager, the velocity field of plasma flows is derived by the differential affine velocity estimator for vector magnetograms. In three cases, the magnetic fluxes evolve to pump net positive, negative, and mixed-sign helicity flux into the corona. The coronal helicity flux is dominantly coming from the shear term that is related to horizontal flux motions, whereas energy flux is dominantly contributed by the emergence term. The shear helicity fluxmore » has a phase delay of 5–14 hr with respect to absolute magnetic flux. The nonlinear curve of coronal energy versus relative helicity identifies the configuration of coronal magnetic fields, which is approximated by a fit of linear force-free fields. The nature of coronal helicity related to the particular pattern of evolving magnetic fluxes at the photosphere has implications for the generation mechanism of two kinds of observed activity in the ARs.« less

Evolution of the magnetic helicity flux during the formation and eruption of flux ropes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romano, P.; Zuccarello, F. P.; Guglielmino, S. L.

We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We foundmore » a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.« less

Performance analysis of a new radial-axial flux machine with SMC cores and ferrite magnets

NASA Astrophysics Data System (ADS)

Liu, Chengcheng; Wang, Youhua; Lei, Gang; Guo, Youguang; Zhu, Jianguo

2017-05-01

Soft magnetic composite (SMC) is a popular material in designing of new 3D flux electrical machines nowadays for it has the merits of isotropic magnetic characteristic, low eddy current loss and high design flexibility over the electric steel. The axial flux machine (AFM) with the extended stator tooth tip both in the radial and circumferential direction is a good example, which has been investigated in the last years. Based on the 3D flux AFM and radial flux machine, this paper proposes a new radial-axial flux machine (RAFM) with SMC cores and ferrite magnets, which has very high torque density though the low cost low magnetic energy ferrite magnet is utilized. Moreover, the cost of RAFM is quite low since the manufacturing cost can be reduced by using the SMC cores and the material cost will be decreased due to the adoption of the ferrite magnets. The 3D finite element method (FEM) is used to calculate the magnetic flux density distribution and electromagnetic parameters. For the core loss calculation, the rotational core loss computation method is used based on the experiment results from previous 3D magnetic tester.

Magnetic Flux Circulation During Dawn-Dusk Oriented Interplanetary Magnetic Field

NASA Technical Reports Server (NTRS)

Mitchell, E. J.; Lopez, R. E.; Fok, M.-C.; Deng, Y.; Wiltberger, M.; Lyon, J.

2010-01-01

Magnetic flux circulation is a primary mode of energy transfer from the solar wind into the ionosphere and inner magnetosphere. For southward interplanetary magnetic field (IMF), magnetic flux circulation is described by the Dungey cycle (dayside merging, night side reconnection, and magnetospheric convection), and both the ionosphere and inner magnetosphere receive energy. For dawn-dusk oriented IMF, magnetic flux circulation is not well understood, and the inner magnetosphere does not receive energy. Several models have been suggested for possible reconnection patterns; the general pattern is: dayside merging; reconnection on the dayside or along the dawn/dusk regions; and, return flow on dayside only. These models are consistent with the lack of energy in the inner magnetosphere. We will present evidence that the Dungey cycle does not explain the energy transfer during dawn-dusk oriented IMF. We will also present evidence of how magnetic flux does circulate during dawn-dusk oriented IMF, specifically how the magnetic flux reconnects and circulates back.

The cancellation of magnetic flux. II - In a decaying active region. [of sun

NASA Technical Reports Server (NTRS)

Martin, S. F.; Livi, S. H. B.; Wang, J.

1985-01-01

H-alpha filtergrams and videomagnetograms are used to study an active region during its period of decay on August 3-8, 1984; the decay had been initiated by a fragmentation process in which very small knots of magnetic flux separated from larger concentration of flux. The disappearance of magnetic flux was always observed when the small fragments of flux encountered other small fragments or concentrations of flux of opposite polarity. Such 'cancellations' are shared by both polarities of magnetic field, and it is deduced that the disappearance of flux occurred either at or within 5 arcsec of the apparent dividing line between the opposite polarities. All of the 22 flares observed during the decay of this region were initiated around sites where magnetic flux was cancelling or was deduced to be cancelling during the flares. It is hypothesized that cancellation was one of the necessary conditions for flaring in this active region.

On Flare-CME Characteristics from Sun to Earth Combining Remote-Sensing Image Data with In Situ Measurements Supported by Modeling

NASA Astrophysics Data System (ADS)

Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin; Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen; Rodriguez, Luciano

2017-07-01

We analyze the well-observed flare and coronal mass ejection (CME) from 1 October 2011 (SOL2011-10-01T09:18) covering the complete chain of effects - from Sun to Earth - to better understand the dynamic evolution of the CME and its embedded magnetic field. We study in detail the solar surface and atmosphere associated with the flare and CME using the Solar Dynamics Observatory (SDO) and ground-based instruments. We also track the CME signature off-limb with combined extreme ultraviolet (EUV) and white-light data from the Solar Terrestrial Relations Observatory (STEREO). By applying the graduated cylindrical shell (GCS) reconstruction method and total mass to stereoscopic STEREO-SOHO ( Solar and Heliospheric Observatory) coronagraph data, we track the temporal and spatial evolution of the CME in the interplanetary space and derive its geometry and 3D mass. We combine the GCS and Lundquist model results to derive the axial flux and helicity of the magnetic cloud (MC) from in situ measurements from Wind. This is compared to nonlinear force-free (NLFF) model results, as well as to the reconnected magnetic flux derived from the flare ribbons (flare reconnection flux) and the magnetic flux encompassed by the associated dimming (dimming flux). We find that magnetic reconnection processes were already ongoing before the start of the impulsive flare phase, adding magnetic flux to the flux rope before its final eruption. The dimming flux increases by more than 25% after the end of the flare, indicating that magnetic flux is still added to the flux rope after eruption. Hence, the derived flare reconnection flux is most probably a lower limit for estimating the magnetic flux within the flux rope. We find that the magnetic helicity and axial magnetic flux are lower in the interplanetary space by ˜ 50% and 75%, respectively, possibly indicating an erosion process. A CME mass increase of 10% is observed over a range of {˜} 4 - 20 R_{⊙}. The temporal evolution of the CME-associated core-dimming regions supports the scenario that fast outflows might supply additional mass to the rear part of the CME.

Three-dimensional prominence-hosting magnetic configurations: Creating a helical magnetic flux rope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, C.; Keppens, R.; Guo, Y.

2014-01-10

The magnetic configuration hosting prominences and their surrounding coronal structure is a key research topic in solar physics. Recent theoretical and observational studies strongly suggest that a helical magnetic flux rope is an essential ingredient to fulfill most of the theoretical and observational requirements for hosting prominences. To understand flux rope formation details and obtain magnetic configurations suitable for future prominence formation studies, we here report on three-dimensional isothermal magnetohydrodynamic simulations including finite gas pressure and gravity. Starting from a magnetohydrostatic corona with a linear force-free bipolar magnetic field, we follow its evolution when introducing vortex flows around the mainmore » polarities and converging flows toward the polarity inversion line near the bottom of the corona. The converging flows bring the feet of different loops together at the polarity inversion line, where magnetic reconnection and flux cancellation happen. Inflow and outflow signatures of the magnetic reconnection process are identified, and thereby the newly formed helical loops wind around preexisting ones so that a complete flux rope grows and ascends. When a macroscopic flux rope is formed, we switch off the driving flows and find that the system relaxes to a stable state containing a helical magnetic flux rope embedded in an overlying arcade structure. A major part of the formed flux rope is threaded by dipped field lines that can stably support prominence matter, while the total mass of the flux rope is in the order of 4-5× 10{sup 14} g.« less

A mobile ferromagnetic shape detection sensor using a Hall sensor array and magnetic imaging.

PubMed

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

This paper presents a mobile Hall sensor array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the mobile Hall sensor array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of mobile Hall sensor array system for actual shape detection. The results prove that the mobile Hall sensor array system is able to perform magnetic imaging in identifying various ferromagnetic materials.

A Mobile Ferromagnetic Shape Detection Sensor Using a Hall Sensor Array and Magnetic Imaging

PubMed Central

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

This paper presents a Mobile Hall Sensor Array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the Mobile Hall Sensor Array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of Mobile Hall Sensor Array system for actual shape detection. The results prove that the Mobile Hall Sensor Array system is able to perform magnetic imaging in identifying various ferromagnetic materials. PMID:22346653

Minnealloy: a new magnetic material with high saturation flux density and low magnetic anisotropy

NASA Astrophysics Data System (ADS)

Mehedi, Md; Jiang, Yanfeng; Suri, Pranav Kumar; Flannigan, David J.; Wang, Jian-Ping

2017-09-01

We are reporting a new soft magnetic material with high saturation magnetic flux density, and low magnetic anisotropy. The new material is a compound of iron, nitrogen and carbon, α‧-Fe8(NC), which has saturation flux density of 2.8  ±  0.15 T and magnetic anisotropy of 46 kJ m-3. The saturation flux density is 27% higher than pure iron, a widely used soft magnetic material. Soft magnetic materials are very important building blocks of motors, generators, inductors, transformers, sensors and write heads of hard disk. The new material will help in the miniaturization and efficiency increment of the next generation of electronic devices.

Magnetic Flux Emergence Along the Solar Cycle

NASA Astrophysics Data System (ADS)

Schmieder, B.; Archontis, V.; Pariat, E.

2014-12-01

Flux emergence plays an important role along the solar cycle. Magnetic flux emergence builds sunspot groups and solar activity. The sunspot groups contribute to the large scale behaviour of the magnetic field over the 11 year cycle and the reversal of the North and South magnetic polarity every 22 years. The leading polarity of sunspot groups is opposite in the North and South hemispheres and reverses for each new solar cycle. However the hemispheric rule shows the conservation of sign of the magnetic helicity with positive and negative magnetic helicity in the South and North hemispheres, respectively. MHD models of emerging flux have been developed over the past twenty years but have not yet succeeded to reproduce solar observations. The emergence of flux occurs through plasma layers of very high gradients of pressure and changing of modes from a large β to a low β plasma (<1). With the new armada of high spatial and temporal resolution instruments on the ground and in space, emergence of magnetic flux is observed in tremendous detail and followed during their transit through the upper atmosphere. Signatures of flux emergence in the corona depend on the pre-existing magnetic configuration and on the strength of the emerging flux. We review in this paper new and established models as well as the recent observations.

Zn Coordination Chemistry:  Development of Benchmark Suites for Geometries, Dipole Moments, and Bond Dissociation Energies and Their Use To Test and Validate Density Functionals and Molecular Orbital Theory.

PubMed

Amin, Elizabeth A; Truhlar, Donald G

2008-01-01

We present nonrelativistic and relativistic benchmark databases (obtained by coupled cluster calculations) of 10 Zn-ligand bond distances, 8 dipole moments, and 12 bond dissociation energies in Zn coordination compounds with O, S, NH3, H2O, OH, SCH3, and H ligands. These are used to test the predictions of 39 density functionals, Hartree-Fock theory, and seven more approximate molecular orbital theories. In the nonrelativisitic case, the M05-2X, B97-2, and mPW1PW functionals emerge as the most accurate ones for this test data, with unitless balanced mean unsigned errors (BMUEs) of 0.33, 0.38, and 0.43, respectively. The best local functionals (i.e., functionals with no Hartree-Fock exchange) are M06-L and τ-HCTH with BMUEs of 0.54 and 0.60, respectively. The popular B3LYP functional has a BMUE of 0.51, only slightly better than the value of 0.54 for the best local functional, which is less expensive. Hartree-Fock theory itself has a BMUE of 1.22. The M05-2X functional has a mean unsigned error of 0.008 Å for bond lengths, 0.19 D for dipole moments, and 4.30 kcal/mol for bond energies. The X3LYP functional has a smaller mean unsigned error (0.007 Å) for bond lengths but has mean unsigned errors of 0.43 D for dipole moments and 5.6 kcal/mol for bond energies. The M06-2X functional has a smaller mean unsigned error (3.3 kcal/mol) for bond energies but has mean unsigned errors of 0.017 Å for bond lengths and 0.37 D for dipole moments. The best of the semiempirical molecular orbital theories are PM3 and PM6, with BMUEs of 1.96 and 2.02, respectively. The ten most accurate functionals from the nonrelativistic benchmark analysis are then tested in relativistic calculations against new benchmarks obtained with coupled-cluster calculations and a relativistic effective core potential, resulting in M05-2X (BMUE = 0.895), PW6B95 (BMUE = 0.90), and B97-2 (BMUE = 0.93) as the top three functionals. We find significant relativistic effects (∼0.01 Å in bond lengths, ∼0.2 D in dipole moments, and ∼4 kcal/mol in Zn-ligand bond energies) that cannot be neglected for accurate modeling, but the same density functionals that do well in all-electron nonrelativistic calculations do well with relativistic effective core potentials. Although most tests are carried out with augmented polarized triple-ζ basis sets, we also carried out some tests with an augmented polarized double-ζ basis set, and we found, on average, that with the smaller basis set DFT has no loss in accuracy for dipole moments and only ∼10% less accurate bond lengths.

Magnetization behavior of RE123 bulk magnets bearing twin seed-crystals in pulsed field magnetization processes

NASA Astrophysics Data System (ADS)

Oka, T.; Miyazaki, T.; Ogawa, J.; Fukui, S.; Sato, T.; Yokoyama, K.; Langer, M.

2016-02-01

Melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were fabricated by the cold seeding method with using single or twin-seed crystals composed of Nd-Ba-Cu-O thin films on MgO substrates. The behavior of the magnetic flux penetration into anisotropic-grown bulk magnets thus fabricated was precisely evaluated during and after the pulsed field magnetization operated at 35 K. These seed crystals were put on the top surfaces of the precursors to grow large grains during the melt-processes. Although we know the magnetic flux motion is restricted by the enhanced pinning effect in temperature ranges lower than 77 K, we observed that flux invasion occurred at applied fields of 3.3 T when the twin seeds were used. This is definitely lower than those of 3.7 T when the single-seeds were employed. This means that the magnetic fluxes are capable of invading into twin-seeded bulk magnets more easily than single-seeded ones. The twin seeds form the different grain growth regions, the narrow-GSR (growth sector region) and wide-GSR, according to the different grain growth directions which are parallel and normal to the rows of seed crystals, respectively. The invading flux measurements revealed that the magnetic flux invades the sample from the wide-GSR prior to the narrow-GSR. It suggests that such anisotropic grain growth leads to different distributions of pinning centers, variations of J c values, and the formation of preferential paths for the invading magnetic fluxes. Using lower applied fields definitely contributed to lowering the heat generation during the PFM process, which, in turn, led to enhanced trapped magnetic fluxes.

How Well Can a Footpoint Tracking Method Estimate the Magnetic Helicity Influx during Flux Emergence?

NASA Astrophysics Data System (ADS)

Choe, Gwangson; Kim, Sunjung; Kim, Kap-Sung; No, Jincheol

2015-08-01

As shown by Démoulin and Berger (2003), the magnetic helicity flux through the solar surface into the solar atmosphere can be exactly calculated if we can trace the motion of footpoints with infinite temporal and spatial resolutions. When there is a magnetic flux transport across the solar surface, the horizontal velocity of footpoints becomes infinite at the polarity inversion line, although the surface integral yielding the helicity flux does not diverge. In practical application, a finite temporal and spatial resolution causes an underestimate of the magnetic helicity flux when a magnetic flux emerges from below the surface, because there is an observational blackout area near a polarity inversion line whether it is pre-existing or newly formed. In this paper, we consider emergence of simple magnetic flux ropes and calculate the supremum of the magnitude of the helicity influx that can be estimated from footpoint tracking. The results depend on the ratio of the resolvable length scale and the flux rope diameter. For a Gold-Hoyle flux rope, in which all field lines are uniformly twisted, the observationally estimated helicity influx would be about 90% of the real influx when the flux rope diameter is one hundred times the spatial resolution (for a large flux rope), and about 45% when it is ten times (for a small flux rope). For Lundquist flux ropes, the errors incurred by observational estimation are smaller than the case of the Gold-Hoyle flux rope, but could be as large as 30% of the real influx. Our calculation suggests that the error in the helicity influx estimate is at least half of the real influx or even larger when small scale magnetic structures (less than 10,000 km) emerge into the solar atmosphere.

Study on magnetic circuit of moving magnet linear compressor

NASA Astrophysics Data System (ADS)

Xia, Ming; Chen, Xiaoping; Chen, Jun

2015-05-01

The moving magnet linear compressors are very popular in the tactical miniature stirling cryocoolers. The magnetic circuit of LFC3600 moving magnet linear compressor, manufactured by Kunming institute of Physics, was studied in this study. Three methods of the analysis theory, numerical calculation and experiment study were applied in the analysis process. The calculated formula of magnetic reluctance and magnetomotive force were given in theoretical analysis model. The magnetic flux density and magnetic flux line were analyzed in numerical analysis model. A testing method was designed to test the magnetic flux density of the linear compressor. When the piston of the motor was in the equilibrium position, the value of the magnetic flux density was at the maximum of 0.27T. The results were almost equal to the ones from numerical analysis.

The Open Flux Problem

NASA Astrophysics Data System (ADS)

Linker, J. A.; Caplan, R. M.; Downs, C.; Riley, P.; Mikic, Z.; Lionello, R.; Henney, C. J.; Arge, C. N.; Liu, Y.; Derosa, M. L.; Yeates, A.; Owens, M. J.

2017-10-01

The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun’s photosphere, where it has been observed for many years. Global maps of the solar magnetic field based on full-disk magnetograms are commonly used as boundary conditions for coronal and solar wind models. Two primary observational constraints on the models are (1) the open field regions in the model should approximately correspond to coronal holes (CHs) observed in emission and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. In this study, we calculate both magnetohydrodynamic and potential field source surface solutions using 14 different magnetic maps produced from five different types of observatory magnetograms, for the time period surrounding 2010 July. We have found that for all of the model/map combinations, models that have CH areas close to observations underestimate the interplanetary magnetic flux, or, conversely, for models to match the interplanetary flux, the modeled open field regions are larger than CHs observed in EUV emission. In an alternative approach, we estimate the open magnetic flux entirely from solar observations by combining automatically detected CHs for Carrington rotation 2098 with observatory synoptic magnetic maps. This approach also underestimates the interplanetary magnetic flux. Our results imply that either typical observatory maps underestimate the Sun’s magnetic flux, or a significant portion of the open magnetic flux is not rooted in regions that are obviously dark in EUV and X-ray emission.

The Open Flux Problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Linker, J. A.; Caplan, R. M.; Downs, C.

The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun’s photosphere, where it has been observed for many years. Global maps of the solar magnetic field based on full-disk magnetograms are commonly used as boundary conditions for coronal and solar wind models. Two primary observational constraints on the models are (1) the open field regions in the model should approximately correspond to coronal holes (CHs) observed in emission and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. Inmore » this study, we calculate both magnetohydrodynamic and potential field source surface solutions using 14 different magnetic maps produced from five different types of observatory magnetograms, for the time period surrounding 2010 July. We have found that for all of the model/map combinations, models that have CH areas close to observations underestimate the interplanetary magnetic flux, or, conversely, for models to match the interplanetary flux, the modeled open field regions are larger than CHs observed in EUV emission. In an alternative approach, we estimate the open magnetic flux entirely from solar observations by combining automatically detected CHs for Carrington rotation 2098 with observatory synoptic magnetic maps. This approach also underestimates the interplanetary magnetic flux. Our results imply that either typical observatory maps underestimate the Sun’s magnetic flux, or a significant portion of the open magnetic flux is not rooted in regions that are obviously dark in EUV and X-ray emission.« less

Magnetic flux ropes at the high-latitude magnetopause

NASA Technical Reports Server (NTRS)

Berchem, Jean; Raeder, Joachim; Ashour-Abdalla, Maha

1995-01-01

We examine the consequences of magnetic reconnection at the high-latitude magnetopause using a three-dimensional global magnetohydrodynamic simulation of the solar wind interaction with the Earth's magnetosphere. Magnetic field lines from the simulation reveal the formation of magnetic flux ropes during periods with northward interplanetary magnetic field. These flux ropes result from multiple reconnection processes between the lobes field lines and draped magnetosheath field lines that are convected around the flank of the magnetosphere. The flux ropes identified in the simulation are consistent with features observed in the magnetic field measured by Hawkeye-1 during some high-latitude magnetopause crossings.

Dual-stage trapped-flux magnet cryostat for measurements at high magnetic fields

DOEpatents

Islam, Zahirul; Das, Ritesh K.; Weinstein, Roy

2015-04-14

A method and a dual-stage trapped-flux magnet cryostat apparatus are provided for implementing enhanced measurements at high magnetic fields. The dual-stage trapped-flux magnet cryostat system includes a trapped-flux magnet (TFM). A sample, for example, a single crystal, is adjustably positioned proximate to the surface of the TFM, using a translation stage such that the distance between the sample and the surface is selectively adjusted. A cryostat is provided with a first separate thermal stage provided for cooling the TFM and with a second separate thermal stage provided for cooling sample.

Magnetic-Flux-Compression Cooling Using Superconductors

NASA Technical Reports Server (NTRS)

Strayer, Donald M.; Israelsson, Ulf E.; Elleman, Daniel D.

1989-01-01

Proposed magnetic-flux-compression refrigeration system produces final-stage temperatures below 4.2 K. More efficient than mechanical and sorption refrigerators at temperatures in this range. Weighs less than comparable liquid-helium-cooled superconducting magnetic refrigeration systems operating below 4.2 K. Magnetic-flux-compression cooling stage combines advantages of newly discovered superconductors with those of cooling by magnetization and demagnetization of paramagnetic salts.

Line-of-sight magnetic flux imbalances caused by electric currents

NASA Technical Reports Server (NTRS)

Gary, G. Allen; Rabin, Douglas

1995-01-01

Several physical and observational effects contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0-15%, depending on the character of the current-carying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other- probably larger- effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.

Solar Open Flux Migration from Pole to Pole: Magnetic Field Reversal.

PubMed

Huang, G-H; Lin, C-H; Lee, L C

2017-08-25

Coronal holes are solar regions with low soft X-ray or low extreme ultraviolet intensities. The magnetic fields from coronal holes extend far away from the Sun, and thus they are identified as regions with open magnetic field lines. Coronal holes are concentrated in the polar regions during the sunspot minimum phase, and spread to lower latitude during the rising phase of solar activity. In this work, we identify coronal holes with outward and inward open magnetic fluxes being in the opposite poles during solar quiet period. We find that during the sunspot rising phase, the outward and inward open fluxes perform pole-to-pole trans-equatorial migrations in opposite directions. The migration of the open fluxes consists of three parts: open flux areas migrating across the equator, new open flux areas generated in the low latitude and migrating poleward, and new open flux areas locally generated in the polar region. All three components contribute to the reversal of magnetic polarity. The percentage of contribution from each component is different for different solar cycle. Our results also show that the sunspot number is positively correlated with the lower-latitude open magnetic flux area, but negatively correlated with the total open flux area.

Studying the Formation and Evolution of Eruptive Solar Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Linton, M.

2017-12-01

Solar magnetic eruptions are dramatic sources of solar activity, and dangerous sources of space weather hazards. Many of these eruptions take the form of magnetic flux ropes, i.e., magnetic fieldlines wrapping around a core magnetic flux tube. Investigating the processes which form these flux ropes both prior to and during eruption, and investigating their evolution after eruption, can give us a critical window into understanding the sources of and processes involved in these eruptions. This presentation will discuss modeling and observational investigations into these various phases of flux rope formation, eruption, and evolution, and will discuss how these different explorations can be used to develop a more complete picture of erupting flux rope dynamics. This work is funded by the NASA Living with a Star program.

Can Polar Fields Explain Missing Open Flux?

NASA Astrophysics Data System (ADS)

Linker, J.; Downs, C.; Caplan, R. M.; Riley, P.; Mikic, Z.; Lionello, R.

2017-12-01

The "open" magnetic field is the portion of the Sun's magnetic field that extends out into the heliosphere and becomes the interplanetary magnetic field (IMF). Both the IMF and the Sun's magnetic field in the photosphere have been measured for many years. In the standard paradigm of coronal structure, the open magnetic field originates primarily in coronal holes. The regions that are magnetically closed trap the coronal plasma and give rise to the streamer belt. This basic picture is qualitatively reproduced by models of coronal structure using photospheric magnetic fields as input. If this paradigm is correct, there are two primary observational constraints on the models: (1) The open field regions in the model should approximately correspond to coronal holes observed in emission, and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. Linker et al. (2017, ApJ, submitted) investigated the July 2010 time period for a range of observatory maps and both PFSS and MHD models. We found that all of the model/map combinations underestimated the interplanetary magnetic flux, unless the modeled open field regions were larger than observed coronal holes. An estimate of the open magnetic flux made entirely from solar observations (combining detected coronal hole boundaries with observatory synoptic magnetic maps) also underestimated the interplanetary magnetic flux. The magnetic field near the Sun's poles is poorly observed and may not be well represented in observatory maps. In this paper, we explore whether an underestimate of the polar magnetic flux during this time period could account for the overall underestimate of open magnetic flux. Research supported by NASA, AFOSR, and NSF.

The importance of electrothermal terms in Ohm's law for magnetized spherical implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davies, J. R., E-mail: jdav@lle.rochester.edu; Betti, R.; Chang, P.-Y.

2015-11-15

The magnetohydrodynamics (MHD) of magnetic-field compression in laser-driven spherical targets is considered. Magnetic-field evolution is cast in terms of an effective fluid velocity, a convective term resulting from resistivity gradients, a resistive diffusion term, and a source term. Effective velocity is the sum of fluid velocity, drift velocity, and heat-flux velocity, given by electron heat flux divided by electron enthalpy density, which has two components: the perpendicular or Nernst velocity and the cross-field velocity. The Nernst velocity compresses the magnetic field as the heat front moves into gas. The cross-field velocity leads to dynamo generation of an azimuthal magnetic field.more » It is proposed that the heat-flux velocity should be flux limited using a “Nernst” flux limiter independent of the thermal flux limiter but should not exceed it. The addition of the MHD routines to the 1D, Lagrangian hydrocode LILAC and the Eulerian version of the 2D hydrocode DRACO is described, and the codes are used to model a magnetized spherical compression on the OMEGA laser. Thermal flux limiting at a shock front is found to cause unphysical electron temperature gradients that lead to large, unphysical magnetic fields caused by the resistivity gradient, so thermal flux limiting in the gas is removed. The Nernst term reduces the benefits of magnetization in inertial fusion. A Nernst flux limiter ≤0.12 is required in the gas in order to agree with measured neutron yield and increases in the neutron-averaged ion temperature caused by magnetization. This corresponds to preventing the Nernst velocity from exceeding the shock velocity, which prevents significant decoupling of the magnetic field and gas compression.« less

A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

NASA Astrophysics Data System (ADS)

Zhou, Difan; Ainslie, Mark D.; Shi, Yunhua; Dennis, Anthony R.; Huang, Kaiyuan; Hull, John R.; Cardwell, David A.; Durrell, John H.

2017-02-01

A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetization. The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g., 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

The YBa2Cu3O7- anomalous second peak and irreversible magnetic field in the magnetization hysteresis cycles

NASA Astrophysics Data System (ADS)

Taoufik, A.; Ramzi, A.; Senoussi, S.; Labrag, A.

2004-05-01

The flux jumps, the second peak and the irreversible magnetic field in the magnetization hysteresis cycles have been investigated in the high temperature superconductor YBa2Cu3O7- single crystals. These cycles were obtained for different temperature values, the applied magnetic fields up to 6 T and the angle between the applied magnetic field and c-axis. The magnetization curves exhibit a remarkable second peak fishtail, this second peak was not observed for the low temperature, but we observed the flux jumps saw tooth. The temperature dependence of the irreversible magnetic field, Hirr, for the applied magnetic field perpendicular to the ab planes is given by an extended expression, Hirr α (1-T/Tc )α, where α is a constant, the Abrikosov flux dynamics can explain this behavior. The Hirr as a function of has been strongly influenced by the flux pinning and the thermally assisted flux motion.

MMS observations of magnetic reconnection signatures of dissipating ion inertial-scale flux ropes associated with dipolarization events

NASA Astrophysics Data System (ADS)

Poh, G.; Slavin, J. A.; Lu, S.; Le, G.; Cassak, P.; Eastwood, J. P.; Ozturk, D. S.; Zou, S.; Nakamura, R.; Baumjohann, W.; Russell, C. T.; Gershman, D. J.; Giles, B. L.; Pollock, C.; Moore, T. E.; Torbert, R. B.; Burch, J. L.

2017-12-01

The formation of flux ropes is thought to be an integral part of the process that may have important consequences for the onset and subsequent rate of reconnection in the tail. Earthward flows, i.e. bursty bulk flows (BBFs), generate dipolarization fronts (DFs) as they interact with the closed magnetic flux in their path. Global hybrid simulations and THEMIS observations have shown that earthward-moving flux ropes can undergo magnetic reconnection with the near-Earth dipole field in the downtail region between the Near Earth Neutral Line and the near-Earth dipole field to create DFs-like signatures. In this study, we analyzed sequential "chains" of earthward-moving, ion-scale flux ropes embedded within DFs observed during MMS first tail season. MMS high-resolution plasma measurements indicate that these earthward flux ropes embedded in DFs have a mean bulk flow velocity and diameter of 250 km/s and 1000 km ( 2‒3 ion inertial length λi), respectively. Magnetic reconnection signatures preceding the flux rope/DF encounter were also observed. As the southward-pointing magnetic field in the leading edge of the flux rope reconnects with the northward-pointing geomagnetic field, the characteristic quadrupolar Hall magnetic field in the ion diffusion region and electron outflow jets in the north-south direction are observed. Our results strongly suggest that the earthward moving flux ropes brake and gradually dissipate due to magnetic reconnection with the near Earth magnetic field. We have also examined the occurrence rate of these dissipating flux ropes/DF events as a function of downtail distances.

THE ROLE OF THE INNER CORONAL NULL POINT IN THE FORMATION AND EVOLUTION OF SOLAR QUIESCENT PROMINENCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y. Z., E-mail: yzzhangmail@sohu.com

2015-02-10

Using a 2.5-dimensional MHD simulation, we investigate the role played by the inner coronal null point in the formation and evolution of solar quiescent prominences. The flux rope is characterized by its magnetic fluxes, the toroidal magnetic flux Φ {sub p} and the poloidal flux Φ{sub ψ}. It is found that for a given Φ {sub p}, the catastrophe does not occur in the flux rope system until Φ{sub ψ} increases to a critical point. Moreover, the magnetic flux of the null point is the maximum value of the magnetic flux in the quadrupole background magnetic field, and represented bymore » ψ {sub N}. The results show that the bigger ψ {sub N} usually corresponds to the smaller catastrophic point, the lower magnetic energy of the flux rope system, and the lesser magnetic energy inside the flux rope. Our results confirm that catastrophic disruption of the prominence occurs more easily when there is a bigger ψ {sub N}. However, ψ {sub N} has little influence on the maximum speed of the coronal mass ejections (CMEs) with an erupted prominence. Thus we argue that a topological configuration with the inner coronal null point is a necessary structure for the formation and evolution of solar quiescent prominences. In conclusion, it is easier for the prominences to form and to erupt as a core part of the CMEs in the magnetic structure with a greater ψ {sub N}.« less

Relationships of a growing magnetic flux region to flares

NASA Technical Reports Server (NTRS)

Martin, S. F.; Bentley, R. D.; Schadee, A.; Antalova, A.; Kucera, A.; Dezso, L.; Gesztelyi, L.; Harvey, K. L.; Jones, H.; Livi, S. H. B.

1984-01-01

The evolution of flare sites at the boundaries of major new and growing magnetic flux regions within complexes of active regions has been analyzed using H-alpha images. A spectrum of possible relationships of growing flux regions to flares is described. An 'intimate' interaction between old and new flux and flare sites occurs at the boundaries of their regions. Forced or 'intimidated' interaction involves new flux pushing older, lower flux density fields toward a neighboring old polarity inversion line, followed by the occurrence of a flare. In 'influential' interaction, magnetic lines of force over an old polarity inversion line reconnect to new emerging flux, and a flare occurs when the magnetic field overlying the filament becomes too weak to prevent its eruption. 'Inconsequential' interaction occurs when a new flux region is too small or has the wrong orientation for creating flare conditions. 'Incidental' interaction involves a flare occurring without any significant relationship to new flux regions.

Spatial Transport of Magnetic Flux Surfaces in Strongly Anisotropic Turbulence

NASA Astrophysics Data System (ADS)

Matthaeus, W. H.; Servidio, S.; Wan, M.; Ruffolo, D. J.; Rappazzo, A. F.; Oughton, S.

2013-12-01

Magnetic flux surfaces afford familiar descriptions of spatial structure, dynamics, and connectivity of magnetic fields, with particular relevance in contexts such as solar coronal flux tubes, magnetic field connectivity in the interplanetary and interstellar medium, as well as in laboratory plasmas and dynamo problems [1-4]. Typical models assume that field-lines are orderly, and flux tubes remain identifiable over macroscopic distances; however, a previous study has shown that flux tubes shred in the presence of fluctuations, typically losing identity after several correlation scales [5]. Here, the structure of magnetic flux surfaces is numerically investigated in a reduced magnetohydrodynamic (RMHD) model of homogeneous turbulence. Short and long-wavelength behavior is studied statistically by propagating magnetic surfaces along the mean field. At small scales magnetic surfaces become complex, experiencing an exponential thinning. At large scales, instead, the magnetic flux undergoes a diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established by means of a multiple scale analysis. Both large and small scales limits are controlled by the Kubo number. These results have consequences for understanding and interpreting processes such as magnetic reconnection and field-line diffusion in plasmas [6]. [1] E. N. Parker, Cosmical Magnetic Fields (Oxford Univ. Press, New York, 1979). [2] J. R. Jokipii and E. N. Parker, Phys. Rev. Lett. 21, 44 (1968). [3] R. Bruno et al., Planet. Space Sci. 49, 1201 (2001). [4] M. N. Rosenbluth et al., Nuclear Fusion 6, 297 (1966). [5] W. H. Matthaeus et al., Phys. Rev. Lett. 75, 2136 (1995). [6] S. Servidio et al., submitted (2013).

Theoretical basal Ca II fluxes for late-type stars: results from magnetic wave models with time-dependent ionization and multi-level radiation treatments

NASA Astrophysics Data System (ADS)

Fawzy, Diaa E.; Stȩpień, K.

2018-03-01

In the current study we present ab initio numerical computations of the generation and propagation of longitudinal waves in magnetic flux tubes embedded in the atmospheres of late-type stars. The interaction between convective turbulence and the magnetic structure is computed and the obtained longitudinal wave energy flux is used in a self-consistent manner to excite the small-scale magnetic flux tubes. In the current study we reduce the number of assumptions made in our previous studies by considering the full magnetic wave energy fluxes and spectra as well as time-dependent ionization (TDI) of hydrogen, employing multi-level Ca II atomic models, and taking into account departures from local thermodynamic equilibrium. Our models employ the recently confirmed value of the mixing-length parameter α=1.8. Regions with strong magnetic fields (magnetic filling factors of up to 50%) are also considered in the current study. The computed Ca II emission fluxes show a strong dependence on the magnetic filling factors, and the effect of time-dependent ionization (TDI) turns out to be very important in the atmospheres of late-type stars heated by acoustic and magnetic waves. The emitted Ca II fluxes with TDI included into the model are decreased by factors that range from 1.4 to 5.5 for G0V and M0V stars, respectively, compared to models that do not consider TDI. The results of our computations are compared with observations. Excellent agreement between the observed and predicted basal flux is obtained. The predicted trend of Ca II emission flux with magnetic filling factor and stellar surface temperature also agrees well with the observations but the calculated maximum fluxes for stars of different spectral types are about two times lower than observations. Though the longitudinal MHD waves considered here are important for chromosphere heating in high activity stars, additional heating mechanism(s) are apparently present.

Siphon flows in isolated magnetic flux tubes. III - The equilibrium path of the flux-tube arch

NASA Technical Reports Server (NTRS)

Thomas, John H.; Montesinos, Benjamin

1990-01-01

It is shown how to calculate the equilibrium path of a thin magnetic flux tube in a stratified, nonmagnetic atmosphere when the flux tube contains a steady siphon flow. The equilbrium path of a static thin flux tube in an infinite stratified atmosphere generally takes the form of a symmetric arch of finite width, with the flux tube becoming vertical at either end of the arch. A siphon flow within the flux tube increases the curvature of the arched equilibrium path in order that the net magnetic tension force can balance the inertial force of the flow, which tries to straighten the flux tube. Thus, a siphon flow reduces the width of the arched equilibrium path, with faster flows producing narrower arches. The effect of the siphon flow on the equilibrium path is generally greater for flux tubes of weaker magnetic field strength. Examples of the equilibrium are shown for both isothemal and adiabatic siphon flows in thin flux tubes in an isothermal external atmosphere.

The correlation between the total magnetic flux and the total jet power

NASA Astrophysics Data System (ADS)

Nokhrina, Elena E.

2017-12-01

Magnetic field threading a black hole ergosphere is believed to play the key role in both driving the powerful relativistic jets observed in active galactic nuclei and extracting the rotational energy from a black hole via Blandford-Znajek process. The magnitude of magnetic field and the magnetic flux in the vicinity of a central black hole is predicted by theoretical models. On the other hand, the magnetic field in a jet can be estimated through measurements of either the core shift effect or the brightness temperature. In both cases the obtained magnetic field is in the radiating domain, so its direct application to the calculation of the magnetic flux needs some theoretical assumptions. In this paper we address the issue of estimating the magnetic flux contained in a jet using the measurements of a core shift effect and of a brightness temperature for the jets, directed almost at the observer. The accurate account for the jet transversal structure allow us to express the magnetic flux through the observed values and an unknown rotation rate of magnetic surfaces. If we assume the sources are in a magnetically arrested disk state, the lower limit for the rotation rate can be obtained. On the other hand, the flux estimate may be tested against the total jet power predicted by the electromagnetic energy extraction model. The resultant expression for power depends logarithmically weakly on an unknown rotation rate. We show that the total jet power estimated through the magnetic flux is in good agreement with the observed power. We also obtain the extremely slow rotation rates, which may be an indication that the majority of the sources considered are not in the magnetically arrested disk state.

The importance of electrothermal terms in Ohm's law for magnetized spherical implosions

DOE PAGES

Davies, J. R.; Betti, R.; Chang, P. -Y.; ...

2015-11-06

The magnetohydrodynamics (MHD) of magnetic-field compression in laser-driven spherical targets is considered. Magnetic-field evolution is cast in terms of an effective fluid velocity, a convective term resulting from resistivity gradients, a resistive diffusion term, and a source term. Effective velocity is the sum of fluid velocity, drift velocity, and heat-flux velocity, given by electron heat flux divided by electron enthalpy density, which has two components: the perpendicular or Nernst velocity and the cross-field velocity. The Nernst velocity compresses the magnetic field as a heat front moves into the gas. The cross-field velocity leads to dynamo generation of an azimuthal magneticmore » field. It is proposed that the heat-flux velocity should be flux limited using a “Nernst” flux limiter independent of the thermal flux limiter but should not exceed it. The addition of MHD routines to the 1-D, Lagrangian hydrocode LILAC and the Eulerian version of the 2-D hydrocode DRACO is described, and the codes are used to model a magnetized spherical compression on the OMEGA laser. Thermal flux limiting at a shock front is found to cause unphysical electron temperature gradients that lead to large, unphysical magnetic fields caused by the resistivity gradient, so thermal flux limiting in the gas is removed. The Nernst term reduces the benefits of magnetization in inertial fusion. In addition, a Nernst flux limiter ≤ 0.12 is required in the gas in order to agree with measured neutron yield and increases in the neutron-averaged ion temperature caused by magnetization. This corresponds to maintaining the Nernst velocity below the shock velocity, which prevents significant decoupling of the magnetic field and gas compression.« less

Signals, resistance to change, and conditioned reinforcement in a multiple schedule.

PubMed

Bell, Matthew C; Gomez, Belen E; Kessler, Kira

2008-06-01

The effect of signals on resistance to change was evaluated using pigeons responding on a three-component multiple schedule. Each component contained a variable-interval initial link followed by a fixed-time terminal link. One component was an unsignaled-delay schedule, and two were equivalent signaled-delay schedules. After baseline training, resistance to change was assessed through (a) extinction and (b) adding free food to the intercomponent interval. During these tests, the signal stimulus from one of the signaled-delay components (SIG-T) was replaced with the initial-link stimulus from that component, converting it to an unsignaled-delay schedule. That signal stimulus was added to the delay period of the unsignaled-delay component (UNS), converting it to a signaled-delay schedule. The remaining signaled component remained unchanged (SIG-C). Resistance-to-change tests showed removing the signal had a minimal effect on resistance to change in the SIG-T component compared to the unchanged SIG-C component except for one block during free-food testing. Adding the signal to the UNS component significantly increased response rates suggesting that component had low response strength. Interestingly, the direction of the effect was in the opposite direction from what is typically observed. Results are consistent with the conclusion that the signal functioned as a conditioned reinforcer and inconsistent with a generalization-decrement explanation.

Flux Transport and the Sun's Global Magnetic Field

NASA Technical Reports Server (NTRS)

Hathaway, David H.

2010-01-01

The Sun s global magnetic field is produced and evolved through the emergence of magnetic flux in active regions and its transport across the solar surface by the axisymmetric differential rotation and meridional flow and the non-axisymmetric convective flows of granulation, supergranulation, and giant cell convection. Maps of the global magnetic field serve as the inner boundary condition for space weather. The photospheric magnetic field and its evolution determine the coronal and solar wind structures through which CMEs must propagate and in which solar energetic particles are accelerated and propagate. Producing magnetic maps which best represent the actual field configuration at any instant requires knowing the magnetic field over the observed hemisphere as well as knowing the flows that transport flux. From our Earth-based vantage point we only observe the front-side hemisphere and each pole is observable for only six months of the year at best. Models for the surface magnetic flux transport can be used to provide updates to the magnetic field configuration in those unseen regions. In this presentation I will describe successes and failures of surface flux transport and present new observations on the structure, the solar cycle variability, and the evolution of the flows involved in magnetic flux transport. I find that supergranules play the dominant role due to their strong flow velocities and long lifetimes. Flux is transported by differential rotation and meridional flow only to the extent that the supergranules participate in those two flows.

Continuous magnetic flux pump

NASA Technical Reports Server (NTRS)

Hildebrandt, A. F.; Elleman, D. D.; Whitmore, F. C. (Inventor)

1966-01-01

A method and means for altering the intensity of a magnetic field by transposing flux from one location to the location desired fro the magnetic field are examined. The device described includes a pair of communicating cavities formed in a block of superconducting material, is dimensioned to be insertable into one of the cavities and to substantially fill the cavity. Magnetic flux is first trapped in the cavities by establishing a magnetic field while the superconducting material is above the critical temperature at which it goes superconducting. Thereafter, the temperature of the material is reduced below the critical value, and then the exciting magnetic field may be removed. By varying the ratios of the areas of the two cavities, it is possible to produce a field having much greater flux density in the second, smaller cavity, into which the flux transposed.

Plasmoids as magnetic flux ropes. [in geomagnetic tail

NASA Technical Reports Server (NTRS)

Moldwin, Mark B.; Hughes, W. J.

1991-01-01

A magnetic flux rope model is developed and used to determine whether the principal axis analysis (PAA) of magnetometer signatures from a single satellite pass is sufficient to obtain the magnetic topology of plasmoids. The model is also used to determine if plasmoid observations are best explained by the flux rope, closed loop, or large-amplitude wave picture. It was found that the principal axis directions is highly dependent on the satellite trajectory through the structure and, therefore, the PAA of magnetometer data from a single satellite pass is insufficient to differentiate between magnetic closed loop and flux rope models. Results also indicate that the flux rope model of plasmoid formation is well suited to unify the observations of various magnetic structures observed by ISEE 3.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, N. B.; Qu, Z. N., E-mail: znqu@ynao.ac.cn

The ensemble empirical mode decomposition (EEMD) analysis is utilized to extract the intrinsic mode functions (IMFs) of the solar mean magnetic field (SMMF) observed at the Wilcox Solar Observatory of Stanford University from 1975 to 2014, and then we analyze the periods of these IMFs as well as the relation of IMFs (SMMF) with some solar activity indices. The two special rotation cycles of 26.6 and 28.5 days should be derived from different magnetic flux elements in the SMMF. The rotation cycle of the weak magnetic flux element in the SMMF is 26.6 days, while the rotation cycle of themore » strong magnetic flux element in the SMMF is 28.5 days. The two rotation periods of the structure of the interplanetary magnetic field near the ecliptic plane are essentially related to weak and strong magnetic flux elements in the SMMF, respectively. The rotation cycle of weak magnetic flux in the SMMF did not vary over the last 40 years because the weak magnetic flux element derived from the weak magnetic activity on the full disk is not influenced by latitudinal migration. Neither the internal rotation of the Sun nor the solar magnetic activity on the disk (including the solar polar fields) causes the annual variation of SMMF. The variation of SMMF at timescales of a solar cycle is more related to weak magnetic activity on the full solar disk.« less

Observations of a Small Interplanetary Magnetic Flux Rope Opening by Interchange Reconnection

NASA Astrophysics Data System (ADS)

Wang, J. M.; Feng, H. Q.; Zhao, G. Q.

2018-01-01

Interchange reconnection, specifically magnetic reconnection between open magnetic fields and closed magnetic flux ropes, plays a major role in the heliospheric magnetic flux budget. It is generally accepted that closed magnetic field lines of interplanetary magnetic flux ropes (IMFRs) can gradually open through reconnection between one of its legs and other open field lines until no closed field lines are left to contribute flux to the heliosphere. In this paper, we report an IMFR associated with a magnetic reconnection exhaust, whereby its closed field lines were opening by a magnetic reconnection event near 1 au. The reconnection exhaust and the following IMFR were observed on 2002 February 2 by both the Wind and ACE spacecraft. Observations on counterstreaming suprathermal electrons revealed that most magnetic field lines of the IMFR were closed, especially those after the front boundary of the IMFR, with both ends connected to the Sun. The unidirectional suprathermal electron strahls before the exhaust manifested the magnetic field lines observed before the exhaust was open. These observations provide direct evidence that closed field lines of IMFRs can be opened by interchange reconnection in interplanetary space. This is the first report of the closed field lines of IMFRs being opened by interchange reconnection in interplanetary space. This type of interplanetary interchange reconnection may pose important implications for balancing the heliospheric flux budget.

Influence of repeated insertion-removal cycles on the force and magnetic flux leakage of magnetic attachments: an in vitro study.

PubMed

Hao, Zhichao; Chao, Yonglie; Meng, Yukun; Yin, Hongmin

2014-08-01

Magnetic attachments are widely used in overdentures and maxillofacial prostheses. Because the patient will routinely have to insert and remove a removable prosthesis, the retentive force and magnetic flux leakage of the magnetic attachments after repeated insertion and removal must be evaluated to assess their clinical performance. The purpose of this in vitro study was to investigate the retentive force and flux leakage of magnetic attachments after repeated insertion and removal. Magfit EX600W magnet-keeper combinations (n=5) were used in this study. After 5000, 10,000, and 20,000 insertion-removal cycles, the retentive force of the magnetic attachments was measured 5 times at a crosshead speed of 5 mm/min with a universal testing machine. Magnetic flux leakage at 3 positions (P1, the upper surface of the magnet; P2, the lower surface of the keeper; and P3, the lateral side of the magnetic attachment set) was evaluated with a gaussmeter. Data were statistically analyzed by 1-way ANOVA (α=.05). The morphology of the abraded surfaces for both the magnet and the keeper was observed with an optical microscope (5×). The mean retentive force decreased significantly after 5000, 10,000, and 20,000 insertion-removal movements (P<.05). Significant differences of flux leakage were also observed at P1 after 5000 cycles and 10,000 cycles, at P2 after 5000 cycles, and at P3 after 5000, 10,000, and 20,000 insertion-removal cycles (P < .05). However, no significant differences in flux leakage were evident after 20,000 cycles at P1 and 10,000 cycles and 20,000 cycles at P2. Repeated insertion and removal influenced the retentive force and magnetic flux leakage of the magnetic attachments. Retentive force decreased significantly after repeated insertion-removal cycles, whereas the variation of magnetic flux leakage depended on refitting cycles and positions of the magnetic attachments. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Dynamo generation of magnetic fields in three-dimensional space - Solar cycle main flux tube formation and reversals

NASA Astrophysics Data System (ADS)

Yoshimura, H.

1983-08-01

The case of the solar magnetic cycle is investigated as a prototype of the dynamo processes involved in the generation of magnetic fields in astrophysics. Magnetohydrodynamic (MHD) equations are solved using a numerical method with a prescribed velocity field in order follow the movement and deformation. It is shown that a simple combination of differential rotation and global convection, given by a linear analysis of fluid dynamics in a rotating sphere, can perpetually create and reverse great magnetic flux tubes encircling the sun. These main flux tubes of the solar cycle are the progenitors of small-scale flux ropes of the solar activity. These findings indicate that magnetic fields can be generated by fluid motions and that MHD equations have a new type of oscillatory solution. It is shown that the solar cycle can be identified with one of these oscillatory solutions. It is proposed that the formation of magnetic flux tubes by streaming plasma flows is a universal mechanism of flux tube formation in astrophysics.

MESSENGER Observations of Extreme Magnetic Tail Loading and Unloading during its Third Flyby of Mercury: Substorms?

NASA Astrophysics Data System (ADS)

Slavin, James A.; Anderson, Brian J.; Baker, Daniel N.; Benna, Mehdi; Gloeckler, George; Krimigis, Stamatios M.; McNutt, Ralph L., Jr.; Schriver, David; Solomon, Sean C.; Zurbuchen, Thomas H.

2010-05-01

During MESSENGER's third flyby of Mercury on September 29, 2009, a variable interplanetary magnetic field produced a series of several minute enhancements of the tail magnetic field by factors of ~ 2 to 3.5. The magnetic field flaring during these intervals indicates that they result from loading of the tail with magnetic flux transferred from the dayside magnetosphere. The unloading intervals were associated with plasmoids and traveling compression regions which are well known signatures of tail reconnection. The peak tail magnetic flux during the smallest loading events equaled 30% of the magnetic flux emanating from Mercury, and may have reached 100% for the largest event. In this case the dayside magnetic shielding is reduced and solar wind flux impacting the surface may be greatly enhanced. Despite the intensity of these events and their similarity to terrestrial substorm magnetic flux dynamics, no energetic charged particles with energies greater than 36 keV were observed. This absence of energetic particles constitutes a deepening puzzle for the view that the Mercury magnetosphere system is undergoing dynamical processes analogous to those at Earth during substorm events.

High strength undiffused brushless machine and method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, John S

2009-04-14

A method and apparatus in which a rotor (11) and a stator (17) define a radial air gap (20) for receiving AC flux and at least one DC excitation coil (23, 24) positioned near the stator end turn to produce DC flux in axial air gaps (21, 22) additive to the AC flux. Side magnets (16) and flux-guiding magnets (14) are provided as boundaries separating the side poles (12a, 12b) of opposite polarity from other portions of the rotor (11) and from each other to define PM poles (12a, 12b) for conveying the DC flux to or from the primarymore » air gap (20) and for inhibiting flux from leaking from said pole portions prior to reaching the primary air gap (20). Side magnets (16), side poles (12a and 12b), flux-guiding magnets (14), ferromagnetic end plates (11c), non-magnetic end plates (12c), and ring bands (37) are optionally provided for performance improvement.« less

Optimization of magnetic flux density measurement using multiple RF receiver coils and multi-echo in MREIT.

PubMed

Jeong, Woo Chul; Chauhan, Munish; Sajib, Saurav Z K; Kim, Hyung Joong; Serša, Igor; Kwon, Oh In; Woo, Eung Je

2014-09-07

Magnetic Resonance Electrical Impedance Tomography (MREIT) is an MRI method that enables mapping of internal conductivity and/or current density via measurements of magnetic flux density signals. The MREIT measures only the z-component of the induced magnetic flux density B = (Bx, By, Bz) by external current injection. The measured noise of Bz complicates recovery of magnetic flux density maps, resulting in lower quality conductivity and current-density maps. We present a new method for more accurate measurement of the spatial gradient of the magnetic flux density gradient (∇ Bz). The method relies on the use of multiple radio-frequency receiver coils and an interleaved multi-echo pulse sequence that acquires multiple sampling points within each repetition time. The noise level of the measured magnetic flux density Bz depends on the decay rate of the signal magnitude, the injection current duration, and the coil sensitivity map. The proposed method uses three key steps. The first step is to determine a representative magnetic flux density gradient from multiple receiver coils by using a weighted combination and by denoising the measured noisy data. The second step is to optimize the magnetic flux density gradient by using multi-echo magnetic flux densities at each pixel in order to reduce the noise level of ∇ Bz and the third step is to remove a random noise component from the recovered ∇ Bz by solving an elliptic partial differential equation in a region of interest. Numerical simulation experiments using a cylindrical phantom model with included regions of low MRI signal to noise ('defects') verified the proposed method. Experimental results using a real phantom experiment, that included three different kinds of anomalies, demonstrated that the proposed method reduced the noise level of the measured magnetic flux density. The quality of the recovered conductivity maps using denoised ∇ Bz data showed that the proposed method reduced the conductivity noise level up to 3-4 times at each anomaly region in comparison to the conventional method.

Modeling Magnetic Flux-Ropes Structures

NASA Astrophysics Data System (ADS)

Nieves-Chinchilla, T.; Linton, M.; Hidalgo, M. A. U.; Vourlidas, A.; Savani, N.; Szabo, A.; Farrugia, C. J.; Yu, W.

2015-12-01

Flux-ropes are usually associated with magnetic structures embedded in the interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature (called Magnetic Clouds, MCs). However, small-scale flux-ropes in the solar wind are also identified with different formation, evolution, and dynamic involved. We present an analytical model to describe magnetic flux-rope topologies. The model is generalized to different grades of complexity. It extends the circular-cylindrical concept of Hidalgo et al. (2002) by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of flux-rope geometrical information and orientation. The generalized model provides flexibility for implementation in 3-D MHD simulations.

Twisted versus braided magnetic flux ropes in coronal geometry. II. Comparative behaviour

NASA Astrophysics Data System (ADS)

Prior, C.; Yeates, A. R.

2016-06-01

Aims: Sigmoidal structures in the solar corona are commonly associated with magnetic flux ropes whose magnetic field lines are twisted about a mutual axis. Their dynamical evolution is well studied, with sufficient twisting leading to large-scale rotation (writhing) and vertical expansion, possibly leading to ejection. Here, we investigate the behaviour of flux ropes whose field lines have more complex entangled/braided configurations. Our hypothesis is that this internal structure will inhibit the large-scale morphological changes. Additionally, we investigate the influence of the background field within which the rope is embedded. Methods: A technique for generating tubular magnetic fields with arbitrary axial geometry and internal structure, introduced in part I of this study, provides the initial conditions for resistive-MHD simulations. The tubular fields are embedded in a linear force-free background, and we consider various internal structures for the tubular field, including both twisted and braided topologies. These embedded flux ropes are then evolved using a 3D MHD code. Results: Firstly, in a background where twisted flux ropes evolve through the expected non-linear writhing and vertical expansion, we find that flux ropes with sufficiently braided/entangled interiors show no such large-scale changes. Secondly, embedding a twisted flux rope in a background field with a sigmoidal inversion line leads to eventual reversal of the large-scale rotation. Thirdly, in some cases a braided flux rope splits due to reconnection into two twisted flux ropes of opposing chirality - a phenomenon previously observed in cylindrical configurations. Conclusions: Sufficiently complex entanglement of the magnetic field lines within a flux rope can suppress large-scale morphological changes of its axis, with magnetic energy reduced instead through reconnection and expansion. The structure of the background magnetic field can significantly affect the changing morphology of a flux rope.

Does High Plasma-β Dynamics ``Load'' Active Regions?

NASA Astrophysics Data System (ADS)

McIntosh, Scott W.

2007-03-01

Using long-duration observations in the He II 304 Å passband of SOHO EIT, we investigate the spatial and temporal appearance of impulsive intensity fluctuations in the pixel light curves. These passband intensity fluctuations come from plasma emitting in the chromosphere, in the transition region, and in the lowest portions of the corona. We see that they are spatially tied to the supergranular scale and that their rate of occurrence is tied to the unsigned imbalance of the magnetic field in which they are observed. The signature of the fluctuations (in space and time) is consistent with their creation by magnetoconvection-forced reconnection, which is driven by the flow field in the high-β plasma. The signature of the intensity fluctuations around an active region suggests that the bulk of the mass and energy going into the active region complex observed in the hotter coronal plasma is supplied by this process, dynamically forcing the looped structure from beneath.

Helicity charging and eruption of magnetic flux from the Sun

NASA Technical Reports Server (NTRS)

Rust, David M.; Kumar, A.

1994-01-01

The ejection of helical toroidal fields from the solar atmosphere and their detection in interplanetary space are described. The discovery that solar magnetic fields are twisted and that they are segregated by hemisphere according to their chirality has important implications for the escape process. The roles played by erupting prominences, coronal mass ejections (CME's) and active region (AR) loops in expressing the escape of magnetic flux and helicity are discussed. Sporadic flux escape associated with filament eruptions accounts for less than one-tenth the flux loss. Azimuthal flux loss by CME's could account for more, but the major contributor to flux escape may be AR loop expansion. It is shown how the transfer of magnetic helicity from the sun's interior into emerged loops ('helicity charging') could be the effective driver of solar eruptions and of flux loss from the sun.

Critical Magnetic Field Strengths for Unipolar Solar Coronal Plumes in Quiet Regions and Coronal Holes?

NASA Astrophysics Data System (ADS)

Avallone, E. A.; Tiwari, S. K.; Panesar, N. K.; Moore, R. L.

2017-12-01

Coronal plumes are sporadic fountain-like structures that are bright in coronal emission. Each is a magnetic funnel rooted in a strong patch of dominant-polarity photospheric magnetic flux surrounded by a predominantly-unipolar magnetic network, either in a quiet region or a coronal hole. The heating processes that make plumes bright evidently involve the magnetic field in the base of the plume, but remain mysterious. Raouafi et al. (2014) inferred from observations that plume heating is a consequence of magnetic reconnection in the base, whereas Wang et al. (2016) showed that plume heating turns on/off from convection-driven convergence/divergence of the base flux. While both papers suggest that the base magnetic flux in their plumes is of mixed polarity, these papers provide no measurements of the abundance and strength of the evolving base flux or consider whether a critical magnetic field strength is required for a plume to become noticeably bright. To address plume production and evolution, we track the plume luminosity and the abundance and strength of the base magnetic flux over the lifetimes of six coronal plumes, using Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 171 Å images and SDO/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms. Three of these plumes are in coronal holes, three are in quiet regions, and each plume exhibits a unipolar base flux. We track the base magnetic flux over each plume's lifetime to affirm that its convergence and divergence respectively coincide with the appearance and disappearance of the plume in 171 Å images. We tentatively find that plume formation requires enough convergence of the base flux to surpass a field strength of ˜300-500 Gauss, and that quiet Sun and coronal-hole plumes both exhibit the same behavior in the response of their luminosity in 171 Å to the strength of the magnetic field in the base.

Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux.

PubMed

Hirono, Yuji; Kharzeev, Dmitri E; Yin, Yi

2016-10-21

We introduce a new mechanism for the chiral magnetic effect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic flux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

Mass ablation and magnetic flux losses through a magnetized plasma-liner wall interface

NASA Astrophysics Data System (ADS)

García-Rubio, F.; Sanz, J.

2017-07-01

The understanding of energy and magnetic flux losses in a magnetized plasma medium confined by a cold wall is of great interest in the success of magnetized liner inertial fusion (MagLIF). In a MagLIF scheme, the fuel is magnetized and subsonically compressed by a cylindrical liner. Magnetic flux conservation is degraded by the presence of gradient-driven transport processes such as thermoelectric effects (Nernst) and magnetic field diffusion. In previous publications [Velikovich et al., Phys. Plasmas 22, 042702 (2015)], the evolution of a hot magnetized plasma in contact with a cold solid wall (liner) was studied using the classical collisional Braginskii's plasma transport equations in one dimension. The Nernst term degraded the magnetic flux conservation, while both thermal energy and magnetic flux losses were reduced with the electron Hall parameter ωeτe with a power-law asymptotic scaling (ωeτe)-1/2. In the analysis made in the present paper, we consider a similar situation, but with the liner being treated differently. Instead of a cold solid wall acting as a heat sink, we model the liner as a cold dense plasma with low thermal conduction (that could represent the cryogenic fuel layer added on the inner surface of the liner in a high-gain MagLIF configuration). Mass ablation comes into play, which adds notably differences to the previous analysis. The direction of the plasma motion is inverted, but the Nernst term still convects the magnetic field towards the liner. Magnetization suppresses the Nernst velocity and improves the magnetic flux conservation. Thermal energy in the hot plasma is lost in heating the ablated material. When the electron Hall parameter is large, mass ablation scales as (ωeτe)-3/10, while both the energy and magnetic flux losses are reduced with a power-law asymptotic scaling (ωeτe)-7/10.

Quasi-static and dynamic magnetic tension forces in arched, line-tied magnetic flux ropes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myers, C. E.; Yamada, M.; Ji, H.

Solar eruptions are often driven by magnetohydrodynamic instabilities such as the torus and kink instabilities that act on line-tied magnetic flux ropes. We designed our recent laboratory experiments to study these eruptive instabilities which have demonstrated the key role of both dynamic (Myers et al 2015 Nature 528 526) and quasi-static (Myers et al 2016 Phys. Plasmas 23 112102) magnetic tension forces in contributing to the equilibrium and stability of line-tied magnetic flux ropes. In our paper, we synthesize these laboratory results and explore the relationship between the dynamic and quasi-static tension forces. And while the quasi-static tension force ismore » found to contribute to the flux rope equilibrium in a number of regimes, the dynamic tension force is substantial mostly in the so-called failed torus regime where magnetic self-organization events prevent the flux rope from erupting.« less

Quasi-static and dynamic magnetic tension forces in arched, line-tied magnetic flux ropes

DOE PAGES

Myers, C. E.; Yamada, M.; Ji, H.; ...

2016-11-22

Solar eruptions are often driven by magnetohydrodynamic instabilities such as the torus and kink instabilities that act on line-tied magnetic flux ropes. We designed our recent laboratory experiments to study these eruptive instabilities which have demonstrated the key role of both dynamic (Myers et al 2015 Nature 528 526) and quasi-static (Myers et al 2016 Phys. Plasmas 23 112102) magnetic tension forces in contributing to the equilibrium and stability of line-tied magnetic flux ropes. In our paper, we synthesize these laboratory results and explore the relationship between the dynamic and quasi-static tension forces. And while the quasi-static tension force ismore » found to contribute to the flux rope equilibrium in a number of regimes, the dynamic tension force is substantial mostly in the so-called failed torus regime where magnetic self-organization events prevent the flux rope from erupting.« less

Magnetic flux amplification by Lenz lenses.

PubMed

Schoenmaker, J; Pirota, K R; Teixeira, J C

2013-08-01

Tailoring magnetic flux distribution is highly desirable in a wide range of applications such as magnetic sensors and biomedicine. In this paper we study the manipulation of induced currents in passive devices in order to engineer the distribution of magnetic flux intensity in a given region. We propose two different approaches, one based on especially designed wire loops (Lenz law) and the other based on solid conductive pieces (eddy currents). The gain of such devices is mainly determined by geometry giving perspective of high amplification. We consistently modeled, simulated, and executed the proposed devices. Doubled magnetic flux intensity is demonstrated experimentally for a moderate aspect ratio.

Magnetic flux amplification by Lenz lenses

NASA Astrophysics Data System (ADS)

Schoenmaker, J.; Pirota, K. R.; Teixeira, J. C.

2013-08-01

Tailoring magnetic flux distribution is highly desirable in a wide range of applications such as magnetic sensors and biomedicine. In this paper we study the manipulation of induced currents in passive devices in order to engineer the distribution of magnetic flux intensity in a given region. We propose two different approaches, one based on especially designed wire loops (Lenz law) and the other based on solid conductive pieces (eddy currents). The gain of such devices is mainly determined by geometry giving perspective of high amplification. We consistently modeled, simulated, and executed the proposed devices. Doubled magnetic flux intensity is demonstrated experimentally for a moderate aspect ratio.

Flux transfer events: Reconnection without separators. [magnetopause

NASA Technical Reports Server (NTRS)

Hesse, M.; Birn, J.; Schindler, K.

1989-01-01

A topological analysis of a simple model magnetic field of a perturbation at the magnetopause modeling an apparent flux transfer event is presented. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause. Although the model field exhibits neutral points, these are not involved in the magnetic connection of the flux tubes. The topological substructure of a localized perturbation is analyzed in a simpler configuration. The presence of both signs of the magnetic field component normal to the magnetopause leads to a linkage of topologically different flux tubes, described as a flux knot, and a filamentary substructure of field lines of different topological types which becomes increasingly complicated for decreasing magnetic shear at the magnetopause.

Flow instabilities of magnetic flux tubes. IV. Flux storage in the solar overshoot region

NASA Astrophysics Data System (ADS)

Işık, E.; Holzwarth, V.

2009-12-01

Context: Flow-induced instabilities of magnetic flux tubes are relevant to the storage of magnetic flux in the interiors of stars with outer convection zones. The stability of magnetic fields in stellar interiors is of importance to the generation and transport of solar and stellar magnetic fields. Aims: We consider the effects of material flows on the dynamics of toroidal magnetic flux tubes located close to the base of the solar convection zone, initially within the overshoot region. The problem is to find the physical conditions in which magnetic flux can be stored for periods comparable to the dynamo amplification time, which is of the order of a few years. Methods: We carry out nonlinear numerical simulations to investigate the stability and dynamics of thin flux tubes subject to perpendicular and longitudinal flows. We compare the simulations with the results of simplified analytical approximations. Results: The longitudinal flow instability induced by the aerodynamic drag force is nonlinear in the sense that the growth rate depends on the perturbation amplitude. This result is consistent with the predictions of linear theory. Numerical simulations without friction show that nonlinear Parker instability can be triggered below the linear threshold of the field strength, when the difference in superadiabaticity along the tube is sufficiently large. A localised downflow acting on a toroidal tube in the overshoot region leads to instability depending on the parameters describing the flow, as well as the magnetic field strength. We determined ranges of the flow parameters for which a linearly Parker-stable magnetic flux tube is stored in the middle of the overshoot region for a period comparable to the dynamo amplification time. Conclusions: The longitudinal flow instability driven by frictional interaction of a flux tube with its surroundings is relevant to determining the storage time of magnetic flux in the solar overshoot region. The residence time for magnetic flux tubes with 2 × 1021 Mx in the convective overshoot layer can be comparable to the dynamo amplification time, provided that the average speed and the duration of an external downflow do not exceed about 50 m s -1 and 100 days, respectively, and that the lateral extension of the flow is smaller than about 10°. Appendix C and movies are only available in electronic form at http://www.aanda.org

Retentive force and magnetic flux leakage of magnetic attachment in various keeper and magnetic assembly combinations.

PubMed

Hasegawa, Mikage; Umekawa, Yoshitada; Nagai, Eiich; Ishigami, Tomohiko

2011-04-01

Magnetic attachments are commonly used for overdentures. However, it can be difficult to identify and provide the same type and size of magnetic assembly and keeper if a repair becomes necessary. Therefore, the size and type may not match. This study evaluated the retentive force and magnetic flux strength and leakage of magnetic attachments in different combinations of keepers and magnetic assemblies. For 6 magnet-keeper combinations using 4 sizes of magnets (GIGAUSS D400, D600, D800, and D1000) (n=5), retentive force was measured 5 times at a crosshead speed of 5 mm/min in a universal testing machine. Magnetic flux strength was measured using a Hall Effect Gaussmeter. Data were statistically analyzed using a 1-way ANOVA, and between-group differences were analyzed with Tukey's HSD post hoc test (α=.05). The mean retentive force of the same-size magnet-keeper combinations was 3.2 N for GIGAUSS D400 and 5.1 N for GIGAUSS D600, but was significantly reduced when using larger magnets (P<.05). Magnetic flux leakage was significantly lower for corresponding size combinations. Size differences influence the retentive force and magnetic flux strength of magnetic attachments. Retentive force decreased due to the closed field structure becoming incomplete and due to magnetic field leakage. Copyright © 2011 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES Magnetic Manipulation of Massless Dirac Fermions in Graphene Quantum Dot

NASA Astrophysics Data System (ADS)

Lin, Xin; Pan, Hui; Xu, Huai-Zhe

2010-12-01

We have theoretically analyzed the quasibound states in a graphene quantum dot (GQD) with a magnetic flux Φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound states of GQD with positive/negative angular momentum shifted upwards / downwards with increasing the magnetic flux. The variation of the quasibound energy depends linearly on the magnetic flux, which is quite different from the parabolic relationship for Schrödinger electrons. The GQD's quasibound states spectrum shows an obvious Aharonov—Bohm (AB) oscillations with the magnetic flux. It is also shown that the quasibound state with energy equal to the barrier height becomes a bound state completely confined in GQD.

Magnetic Energy and Helicity in Two Emerging Active Regions in the Sun

NASA Technical Reports Server (NTRS)

Liu, Y.; Schuck, P. W.

2012-01-01

The magnetic energy and relative magnetic helicity in two emerging solar active regions, AR 11072 and AR 11158,are studied. They are computed by integrating over time the energy and relative helicity fluxes across the photosphere. The fluxes consist of two components: one from photospheric tangential flows that shear and braid field lines (shear term), the other from normal flows that advect magnetic flux into the corona (emergence term). For these active regions: (1) relative magnetic helicity in the active-region corona is mainly contributed by the shear term,(2) helicity fluxes from the emergence and the shear terms have the same sign, (3) magnetic energy in the corona (including both potential energy and free energy) is mainly contributed by the emergence term, and(4) energy fluxes from the emergence term and the shear term evolved consistently in phase during the entire flux emergence course.We also examine the apparent tangential velocity derived by tracking field-line footpoints using a simple tracking method. It is found that this velocity is more consistent with tangential plasma velocity than with the flux transport velocity, which agrees with the conclusion by Schuck.

Fast flux locked loop

DOEpatents

Ganther, Jr., Kenneth R.; Snapp, Lowell D.

2002-09-10

A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.

Estimation of the Magnetic Flux Emergence Rate in the Quiet Sun from Sunrise Data

NASA Astrophysics Data System (ADS)

Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller, T. L.

2017-03-01

Small-scale internetwork (IN) features are thought to be the major source of fresh magnetic flux in the quiet Sun. During its first science flight in 2009, the balloon-borne observatory Sunrise captured images of the magnetic fields in the quiet Sun at a high spatial resolution. Using these data we measure the rate at which the IN features bring magnetic flux to the solar surface. In a previous paper it was found that the lowest magnetic flux in small-scale features detected using the Sunrise observations is 9 × 1014 Mx. This is nearly an order of magnitude smaller than the smallest fluxes of features detected in observations from the Hinode satellite. In this paper, we compute the flux emergence rate (FER) by accounting for such small fluxes, which was not possible before Sunrise. By tracking the features with fluxes in the range {10}15{--}{10}18 Mx, we measure an FER of 1100 {Mx} {{cm}}-2 {{day}}-1. The smaller features with fluxes ≤slant {10}16 Mx are found to be the dominant contributors to the solar magnetic flux. The FER found here is an order of magnitude higher than the rate from Hinode, obtained with a similar feature tracking technique. A wider comparison with the literature shows, however, that the exact technique of determining the rate of the appearance of new flux can lead to results that differ by up to two orders of magnitude, even when applied to similar data. The causes of this discrepancy are discussed and first qualitative explanations proposed.

Relativistic jets without large-scale magnetic fields

NASA Astrophysics Data System (ADS)

Parfrey, K.; Giannios, D.; Beloborodov, A.

2014-07-01

The canonical model of relativistic jets from black holes requires a large-scale ordered magnetic field to provide a significant magnetic flux through the ergosphere--in the Blandford-Znajek process, the jet power scales with the square of the magnetic flux. In many jet systems the presence of the required flux in the environment of the central engine is questionable. I will describe an alternative scenario, in which jets are produced by the continuous sequential accretion of small magnetic loops. The magnetic energy stored in these coronal flux systems is amplified by the differential rotation of the accretion disc and by the rotating spacetime of the black hole, leading to runaway field line inflation, magnetic reconnection in thin current layers, and the ejection of discrete bubbles of Poynting-flux-dominated plasma. For illustration I will show the results of general-relativistic force-free electrodynamic simulations of rotating black hole coronae, performed using a new resistivity model. The dissipation of magnetic energy by coronal reconnection events, as demonstrated in these simulations, is a potential source of the observed high-energy emission from accreting compact objects.

Surface flux density distribution characteristics of bulk high- Tc superconductor in external magnetic field

NASA Astrophysics Data System (ADS)

Torii, S.; Yuasa, K.

2004-10-01

Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

Magnetic properties measurement of soft magnetic composite material (SOMALOY 700) by using 3-D tester

NASA Astrophysics Data System (ADS)

Asari, Ashraf; Guo, Youguang; Zhu, Jianguo

2017-08-01

Core losses of rotating electrical machine can be predicted by identifying the magnetic properties of the magnetic material. The magnetic properties should be properly measured since there are some variations of vector flux density in the rotating machine. In this paper, the SOMALOY 700 material has been measured under x, y and z- axes flux density penetration by using the 3-D tester. The calibrated sensing coils are used in detecting the flux densities which have been generated by the Labview software. The measured sensing voltages are used in obtaining the magnetic properties of the sample such as magnetic flux density B, magnetic field strength H, hysteresis loop which can be used to calculate the total core loss of the sample. The results of the measurement are analyzed by using the Mathcad software before being compared to another material.

Method for determining the hardness of strain hardening articles of tungsten-nickel-iron alloy

DOEpatents

Wallace, Steven A.

1984-01-01

The present invention is directed to a rapid nondestructive method for determining the extent of strain hardening in an article of tungsten-nickel-iron alloy. The method comprises saturating the article with a magnetic field from a permanent magnet, measuring the magnetic flux emanating from the article, comparing the measurements of the magnetic flux emanating from the article with measured magnetic fluxes from similarly shaped standards of the alloy with known amounts of strain hardening to determine the hardness.

Coronal Holes and Magnetic Flux Ropes Interweaving Solar Cycles

NASA Astrophysics Data System (ADS)

Lowder, Chris; Yeates, Anthony; Leamon, Robert; Qiu, Jiong

2016-10-01

Coronal holes, dark patches observed in solar observations in extreme ultraviolet and x-ray wavelengths, provide an excellent proxy for regions of open magnetic field rooted near the photosphere. Through a multi-instrument approach, including SDO data, we are able to stitch together high resolution maps of coronal hole boundaries spanning the past two solar activity cycles. These observational results are used in conjunction with models of open magnetic field to probe physical solar parameters. Magnetic flux ropes are commonly defined as bundles of solar magnetic field lines, twisting around a common axis. Photospheric surface flows and magnetic reconnection work in conjunction to form these ropes, storing magnetic stresses until eruption. With an automated methodology to identify flux ropes within observationally driven magnetofrictional simulations, we can study their properties in detail. Of particular interest is a solar-cycle length statistical description of eruption rates, spatial distribution, magnetic orientation, flux, and helicity. Coronal hole observations can provide useful data about the distribution of the fast solar wind, with magnetic flux ropes yielding clues as to ejected magnetic field and the resulting space weather geo-effectiveness. With both of these cycle-spanning datasets, we can begin to form a more detailed picture of the evolution and consequences of both sets of solar magnetic features.

Embedding Circular Force-Free Flux Ropes in Potential Magnetic Fields

NASA Astrophysics Data System (ADS)

Titov, V. S.; Torok, T.; Mikic, Z.; Linker, J.

2013-12-01

We propose a method for constructing approximate force-free equilibria in active regions that locally have a potential bipolar-type magnetic field with a thin force-free flux rope embedded inside it. The flux rope has a circular-arc axis and circular cross-section in which the interior magnetic field is predominantly toroidal (axial). Its magnetic pressure is balanced outside by that of the poloidal (azimuthal) field created at the boundary by the electric current sheathing the flux rope. To facilitate the implementation of the method in our numerical magnetohydrodynamic (MHD) code, the entire solution is described in terms of the vector potential of the magnetic field. The parameters of the flux rope can be chosen so that a subsequent MHD relaxation of the constructed configuration under line-tied conditions at the boundary provides a numerically exact equilibrium. Such equilibria are an approximation for the magnetic configuration preceding solar eruptions, which can be triggered in our model by imposing suitable photospheric flows beneath the flux rope. The proposed method is a useful tool for constructing pre-eruption magnetic fields in data-driven simulations of solar active events. Research supported by NASA's Heliophysics Theory and LWS Programs, and NSF/SHINE and NSF/FESD.

Solar Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

2003-01-01

We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths > approx. 100 G, (2) approx. 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles.

Solar Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Moore, R. L.; Falconer, D. A.; Porter, J. G.; Hathaway, D. H.

2003-01-01

We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths greater than approximately - 100 G, (2) approximately 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles.

Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Y.; Pariat, E.; Moraitis, K.

We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twistmore » multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.« less

An Evaluation of Electric Motors for Ship Propulsion

DTIC Science & Technology

2003-06-01

AIM). Permanent magnet motors are more power dense than a comparatively sized in- duction motor. The permanent magnet motor has been chosen to...study. They include the axial flux, the ra- dial flux, and the transverse flux permanent magnet motors . Each motor has its unique advantages...to be ideal for ship propulsion, work is ongoing to develop the PMSM for ship propulsion. Permanent magnet motors are expected to have significant

Method for determining transport critical current densities and flux penetration depth in bulk superconductors

NASA Technical Reports Server (NTRS)

Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

1992-01-01

A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

SQUIDs De-fluxing Using a Decaying AC Magnetic Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matlashov, Andrei Nikolaevich; Semenov, Vasili Kirilovich; Anderson, Bill

Flux trapping is the Achilles’ heel of all superconductor electronics. The most direct way to avoid flux trapping is a prevention of superconductor circuits from exposure to magnetic fields. Unfortunately this is not feasible if the circuits must be exposed to a strong DC magnetic field even for a short period of time. For example, such unavoidable exposures take place in superparamagnetic relaxation measurements (SPMR) and ultra-low field magnetic resonance imaging (ULF MRI) using unshielded thin-film SQUID-based gradiometers. Unshielded SQUIDs stop working after being exposed to DC magnetic fields of only a few Gauss in strength. In this paper wemore » present experimental results with de-fluxing of planar thin-film LTS SQUID-based gradiometers using a strong decaying AC magnetic field. We used four commercial G136 gradiometers for SPMR measurements with up to a 10 mT magnetizing field. Strong 12.9 kHz decaying magnetic field pulses reliably return SQUIDs to normal operation 50 ms after zeroing the DC magnetizing field. This new AC de-fluxing method was also successfully tested with seven other different types of LTS SQUID sensors and has been shown to dissipate extremely low energy.« less

Colliding Magnetic Flux Ropes and Quasi-Separatrix Layers in a Laboratory Plasma

NASA Astrophysics Data System (ADS)

Lawrence, Eric Eugene

An experimental study of the dynamics of colliding magnetic flux ropes and the magnetic reconnection that occurs during these collisions is presented. A magnetic flux rope is a bundle of twisted magnetic field lines that is ubiquitous in space and solar plasmas. The flux ropes are created in the Large Plasma Device (LAPD) using two heated lanthanum hexaboride (LaB6) cathodes that inject currents into the background plasma. The currents are initially parallel to the background magnetic field. The azimuthal field of each current together with the background axial field create helical twisted flux ropes. It is found that the flux ropes rotate in time (corkscrew) and collide with each other. During a collision, antiparallel magnetic fields can undergo magnetic reconnection. When these collisions occur, we observe current layers flowing in the opposite direction of the injected current, a signatuare of reconnection. Analysis of the three-dimensional magnetic field lines shows the existence of quasi-separatrix layers (QSLs). These are regions in the magnetic configuration where there are large spatial gradients in the connectivity of field line footpoints in the boundary surfaces. QSLs are thought to be favorable sites for magnetic reconnection. It is shown that the location and shape of the QSL is similar to what is seen in simulations of merging flux ropes. Furthermore, the field line structure of the QSL is similar to that of a twisted hyperbolic flux tube (HFT). An HFT is a type of QSL that has been shown to be a preferred site for current sheet formation in simulations of interacting coronal loops. The HFT in this experiment is found to be generally near the reverse current layers, although the agreement is not perfect. Looking at the time evolution of the QSL, we find that the QSL cross-sectional area grows and contracts at the same time that the flux ropes collide and that the reverse current layers appear. Analysis of the field line motion shows that, during reconnection, bundles of field lines rapidly flip across the QSLs. This is analagous to the way that field lines are pushed across a separatrix in 2D reconnection.

Generation Mechanism for Interlinked Flux Tubes on the Magnetopause

NASA Astrophysics Data System (ADS)

Farinas Perez, G.; Cardoso, F. R.; Sibeck, D.; Gonzalez, W. D.; Facskó, G.; Coxon, J. C.; Pembroke, A. D.

2018-02-01

We use a global magnetohydrodynamics simulation to analyze transient magnetic reconnection processes at the magnetopause. The solar wind conditions have been kept constant, and an interplanetary magnetic field with large duskward BY and southward BZ components has been imposed. Five flux transfer events (FTEs) with clear bipolar magnetic field signatures have been observed. We observed a peculiar structure defined as interlinked flux tubes (IFTs) in the first and fourth FTE, which had very different generation mechanisms. The first FTE originates as an IFTs and remains with this configuration until its final moment. However, the fourth FTE develops as a classical flux rope but changes its 3-D magnetic configuration to that of IFTs. This work studies the mechanism for generating IFTs. The growth of the resistive tearing instability has been identified as the cause for the first IFTs formation. We believe that the instability has been triggered by the accumulation of interplanetary magnetic field at the subsolar point where the grid resolution is very high. The evidence shows that two new reconnection lines form northward and southward of the subsolar region. The IFTs have been generated with all the classical signatures of a single flux rope. The other IFTs detected in the fourth FTE developed as a result of magnetic reconnection inside its complex and twisted magnetic fields, which leads to a change in the magnetic configuration from a flux rope of twisted magnetic field lines to IFTs.

Studying the Transfer of Magnetic Helicity in Solar Active Regions with the Connectivity-based Helicity Flux Density Method

NASA Astrophysics Data System (ADS)

Dalmasse, K.; Pariat, É.; Valori, G.; Jing, J.; Démoulin, P.

2018-01-01

In the solar corona, magnetic helicity slowly and continuously accumulates in response to plasma flows tangential to the photosphere and magnetic flux emergence through it. Analyzing this transfer of magnetic helicity is key for identifying its role in the dynamics of active regions (ARs). The connectivity-based helicity flux density method was recently developed for studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity, which allows it to faithfully track the photospheric flux of magnetic helicity. Because the magnetic field is not measured in the solar corona, modeled 3D solutions obtained from force-free magnetic field extrapolations must be used to derive the magnetic connectivity. Different extrapolation methods can lead to markedly different 3D magnetic field connectivities, thus questioning the reliability of the connectivity-based approach in observational applications. We address these concerns by applying this method to the isolated and internally complex AR 11158 with different magnetic field extrapolation models. We show that the connectivity-based calculations are robust to different extrapolation methods, in particular with regard to identifying regions of opposite magnetic helicity flux. We conclude that the connectivity-based approach can be reliably used in observational analyses and is a promising tool for studying the transfer of magnetic helicity in ARs and relating it to their flaring activity.

Theory of flux cutting and flux transport at the critical current of a type-II superconducting cylindrical wire

NASA Astrophysics Data System (ADS)

Clem, John R.

2011-06-01

I introduce a critical-state theory incorporating both flux cutting and flux transport to calculate the magnetic-field and current-density distributions inside a type-II superconducting cylinder at its critical current in a longitudinal applied magnetic field. The theory is an extension of the elliptic critical-state model introduced by Romero-Salazar and Pérez-Rodríguez. The vortex dynamics depend in detail on two nonlinear effective resistivities for flux cutting (ρ∥) and flux flow (ρ⊥), and their ratio r=ρ∥/ρ⊥. When r<1, the low relative efficiency of flux cutting in reducing the magnitude of the internal magnetic-flux density leads to a paramagnetic longitudinal magnetic moment. As a model for understanding the experimentally observed interrelationship between the critical currents for flux cutting and depinning, I calculate the forces on a helical vortex arc stretched between two pinning centers when the vortex is subjected to a current density of arbitrary angle ϕ. Simultaneous initiation of flux cutting and flux transport occurs at the critical current density Jc(ϕ) that makes the vortex arc unstable.

Flux-Feedback Magnetic-Suspension Actuator

NASA Technical Reports Server (NTRS)

Groom, Nelson J.

1990-01-01

Flux-feedback magnetic-suspension actuator provides magnetic suspension and control forces having linear transfer characteristics between force command and force output over large range of gaps. Hall-effect devices used as sensors for electronic feedback circuit controlling currents flowing in electromagnetic windings to maintain flux linking suspended element at substantially constant value independent of changes in length of gap. Technique provides effective method for maintenance of constant flux density in gap and simpler than previous methods. Applications include magnetic actuators for control of shapes and figures of antennas and of precise segmented reflectors, magnetic suspensions in devices for storage of angular momentum and/or kinetic energy, and systems for control, pointing, and isolation of instruments.

Lamination effects on a 3D model of the magnetic core of power transformers

NASA Astrophysics Data System (ADS)

Poveda-Lerma, Antonio; Serrano-Callergues, Guillermo; Riera-Guasp, Martin; Pineda-Sanchez, Manuel; Puche-Panadero, Ruben; Perez-Cruz, Juan

2017-12-01

In this paper the lamination effect on the model of a power transformer's core with stacked E-I structure is analyzed. The distribution of the magnetic flux in the laminations depends on the stacking method. In this work it is shown, using a 3D FEM model and an experimental prototype, that the non-uniform distribution of the flux in a laminated E-I core with alternate-lap joint stack increases substantially the average value of the magnetic flux density in the core, compared with a butt joint stack. Both the simulated model and the experimental tests show that the presence of constructive air-gaps in the E-I junctions gives rise to a zig-zag flux in the depth direction. This inter-lamination flux reduces the magnetic flux density in the I-pieces and increases substantially the magnetic flux density in the E-pieces, with highly saturated points that traditional 2D analysis cannot reproduce. The relation between the number of laminations included in the model, and the computational resourses needed to build it, is also evaluated in this work.

Degradation Behavior of the HTS Bulk Magnet in Cryocooler System with Cyclic Temperature Variation

NASA Astrophysics Data System (ADS)

Okuno, K.; Sawa, K.; Iwasa, Y.

2006-03-01

This paper presents a change of magnetic flux trapped in the YBCO bulk magnet under thermal excursions. We have supposed a new cryocooler system for the high temperature superconducting(HTS) bulk magnet in which the thermal cycles are generated. From the past research, it was found that the trapped flux mainly deteriorated at the first temperature rise, but a large change of the trapped flux was not seen at the first temperature descent and following thermal cycles. Degradation of the trapped flux by the first temperature-rise was explained by using the bean model. Moreover we proposed the model which does not have a current distribution constant. In this paper, we examined a change of magnetic field in each part of the bulk in detail. In addition, we applied attention to the change of the trapped flux after the first temperature rise. Although there is no big change of the trapped flux after the first temperature-rise, it is decreasing slowly. This cause is considered as influence of the flux creep, but its decay is more rapid than usual.

Analytical Modeling of a Double-Sided Flux Concentrating E-Core Transverse Flux Machine with Pole Windings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muljadi, Eduard; Hasan, Iftekhar; Husain, Tausif

In this paper, a nonlinear analytical model based on the Magnetic Equivalent Circuit (MEC) method is developed for a double-sided E-Core Transverse Flux Machine (TFM). The proposed TFM has a cylindrical rotor, sandwiched between E-core stators on both sides. Ferrite magnets are used in the rotor with flux concentrating design to attain high airgap flux density, better magnet utilization, and higher torque density. The MEC model was developed using a series-parallel combination of flux tubes to estimate the reluctance network for different parts of the machine including air gaps, permanent magnets, and the stator and rotor ferromagnetic materials, in amore » two-dimensional (2-D) frame. An iterative Gauss-Siedel method is integrated with the MEC model to capture the effects of magnetic saturation. A single phase, 1 kW, 400 rpm E-Core TFM is analytically modeled and its results for flux linkage, no-load EMF, and generated torque, are verified with Finite Element Analysis (FEA). The analytical model significantly reduces the computation time while estimating results with less than 10 percent error.« less

Evaluation of magnetic flux distribution from magnetic domains in [Co/Pd] nanowires by magnetic domain scope method using contact-scanning of tunneling magnetoresistive sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okuda, Mitsunobu, E-mail: okuda.m-ky@nhk.or.jp; Miyamoto, Yasuyoshi; Miyashita, Eiichi

2014-05-07

Current-driven magnetic domain wall motions in magnetic nanowires have attracted great interests for physical studies and engineering applications. The magnetic force microscope (MFM) is widely used for indirect verification of domain locations in nanowires, where relative magnetic force between the local domains and the MFM probe is used for detection. However, there is an occasional problem that the magnetic moments of MFM probe influenced and/or rotated the magnetic states in the low-moment nanowires. To solve this issue, the “magnetic domain scope for wide area with nano-order resolution (nano-MDS)” method has been proposed recently that could detect the magnetic flux distributionmore » from the specimen directly by scanning of tunneling magnetoresistive field sensor. In this study, magnetic domain structure in nanowires was investigated by both MFM and nano-MDS, and the leakage magnetic flux density from the nanowires was measured quantitatively by nano-MDS. Specimen nanowires consisted from [Co (0.3)/Pd (1.2)]{sub 21}/Ru(3) films (units in nm) with perpendicular magnetic anisotropy were fabricated onto Si substrates by dual ion beam sputtering and e-beam lithography. The length and the width of the fabricated nanowires are 20 μm and 150 nm. We have succeeded to obtain not only the remanent domain images with the detection of up and down magnetizations as similar as those by MFM but also magnetic flux density distribution from nanowires directly by nano-MDS. The obtained value of maximum leakage magnetic flux by nano-MDS is in good agreement with that of coercivity by magneto-optical Kerr effect microscopy. By changing the protective diamond-like-carbon film thickness on tunneling magnetoresistive sensor, the three-dimensional spatial distribution of leakage magnetic flux could be evaluated.« less

Experimental Verification of the Kruskal-Shafranov Stability Limit in Line-Tied Partial Toroidal Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oz, E.; Myers, C. E.; Yamada, M.

2011-07-19

The stability properties of partial toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas, 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kinkmore » instability. Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., qa = 1).« less

Experimental verification of the Kruskal-Shafranov stability limit in line-tied partial-toroidal plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oz, E.; Myers, C. E.; Yamada, M.

2011-10-15

The stability properties of partial-toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kink instability.more » Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., q{sub a} = 1).« less

Measurements of the Canonical Helicity Evolution of a Gyrating Kinked Flux Rope

NASA Astrophysics Data System (ADS)

von der Linden, J.; Sears, J.; Intrator, T.; You, S.

2017-12-01

Magnetic structures in the solar corona and planetary magnetospheres are often modelled as magnetic flux ropes governed by magnetohydrodynamics (MHD); however, inside these structures, as exhibited in reconnection, conversions between magnetic and kinetic energies occur over a wide range of scales. Flux ropes based on the flux of canonical momentum circulation extend the flux rope concept to include effects of finite particle momentum and present the distinct advantage of reconciling all plasma regimes - e.g. kinetic, two-fluid, and MHD - with the topological concept of helicity: twists, writhes, and linkages. This presentation shows the first visualization and analysis of the 3D dynamics of canonical flux ropes and their relative helicity evolution from laboratory measurements. Ion and electron canonical flux ropes are visualized from a dataset of Mach, triple, and Ḃ probe measurements at over 10,000 spatial locations of a gyrating kinked flux rope. The flux ropes co-gyrate with the peak density and electron temperature in and out of a measurement volume. The electron and ion canonical flux ropes twist with opposite handedness and the ion flux ropes writhe around the electron flux ropes. The relative cross helicity between the magnetic and ion flow vorticity flux ropes dominates the relative ion canonical helicity and is anti-correlated with the relative magnetic helicity. The 3D nature of the kink and a reverse eddy current affect the helicity evolution. This work is supported by DOE Grant DE-SC0010340 and the DOE Office of Science Graduate Student Research Program and prepared in part by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-735426

Testing a new flux rope model using the HELCATS CME catalogue

NASA Astrophysics Data System (ADS)

Rouillard, Alexis Paul; Lavarra, Michael

2017-04-01

We present a magnetically-driven flux rope model that computes the forces acting on a twisted magnetic flux rope from the Sun to 1AU. This model assumes a more realistic flux rope geometry than assumed before by these types of models. The balance of force is computed in an analogous manner to the well-known Chen flux-rope model. The 3-D vector components of the magnetic field measured by a probe flying through the flux rope can be extracted for any flux rope orientation imposed near the Sun. We test this model through a parametric study and a systematic comparison of the model with the HELCATS catalogues (imagery and in situ). We also report on our investigations of other physical mechanisms such as the shift of flux-surfaces associated with the magnetic forces acting to accelerate the flux rope from the lower to upper corona. Finally, we present an evaluation of this model for space-weather predictions. This work was partly funded by the HELCATS project under the FP7 EU contract number 606692.

Heat flux viscosity in collisional magnetized plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, C., E-mail: cliu@pppl.gov; Fox, W.; Bhattacharjee, A.

2015-05-15

Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through themore » generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.« less

A dynamic magnetic tension force as the cause of failed solar eruptions

DOE Data Explorer

Myers, Clayton E. [Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); ] (ORCID:0000000345398406); Yamada, Maasaki [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000349961649); Ji, Hantao [Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China] (ORCID:0000000196009963); Yoo, Jongsoo [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:0000000338811995); Fox, William [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)] (ORCID:000000016289858X); Jara-Almonte, Jonathan [Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); ] (ORCID:0000000307606198); Savcheva, Antonia [Harvard†“ Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA] (ORCID:000000025598046X); DeLuca, Edward E. [Harvard†“ Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA] (ORCID:0000000174162895)

2015-12-11

Coronal mass ejections are solar eruptions driven by a sudden release of magnetic energy stored in the Sun’s corona. In many cases, this magnetic energy is stored in long-lived, arched structures called magnetic flux ropes. When a flux rope destabilizes, it can either erupt and produce a coronal mass ejection or fail and collapse back towards the Sun. The prevailing belief is that the outcome of a given event is determined by a magnetohydrodynamic force imbalance called the torus instability. This belief is challenged, however, by observations indicating that torus-unstable flux ropes sometimes fail to erupt. This contradiction has not yet been resolved because of a lack of coronal magnetic field measurements and the limitations of idealized numerical modelling. Here we report the results of a laboratory experiment that reveal a previously unknown eruption criterion below which torus-unstable flux ropes fail to erupt. We find that such ‘failed torus’ events occur when the guide magnetic field (that is, the ambient field that runs toroidally along the flux rope) is strong enough to prevent the flux rope from kinking. Under these conditions, the guide field interacts with electric currents in the flux rope to produce a dynamic toroidal field tension force that halts the eruption. This magnetic tension force is missing from existing eruption models, which is why such models cannot explain or predict failed torus events.

Magnetically-enhanced open string pair production

NASA Astrophysics Data System (ADS)

Lu, J. X.

2017-12-01

We consider the stringy interaction between two parallel stacks of D3 branes placed at a separation. Each stack of D3 branes in a similar fashion carry an electric flux and a magnetic flux with the two sharing no common field strength index. The interaction amplitude has an imaginary part, giving rise to the Schwinger-like pair production of open strings. We find a significantly enhanced rate of this production when the two electric fluxes are almost identical and the brane separation is on the order of string scale. This enhancement will be largest if the two magnetic fluxes are opposite in direction. This novel enhancement results from the interplay of the non-perturbative Schwinger-type pair production due to the electric flux and the stringy tachyon due to the magnetic flux, and may have realistic physical applications.

A magnetic flux leakage and magnetostrictive guided wave hybrid transducer for detecting bridge cables.

PubMed

Xu, Jiang; Wu, Xinjun; Cheng, Cheng; Ben, Anran

2012-01-01

Condition assessment of cables has gained considerable attention for the bridge safety. A magnetic flux leakage and magnetostrictive guided wave hybrid transducer is provided to inspect bridge cables. The similarities and differences between the two methods are investigated. The hybrid transducer for bridge cables consists of an aluminum framework, climbing modules, embedded magnetizers and a ribbon coil. The static axial magnetic field provided by the magnetizers meets the needs of the magnetic flux leakage testing and the magnetostrictive guided wave testing. The magnetizers also provide the attraction for the climbing modules. In the magnetic flux leakage testing for the free length of cable, the coil induces the axial leakage magnetic field. In the magnetostrictive guided wave testing for the anchorage zone, the coil provides a pulse high power variational magnetic field for generating guided waves; the coil induces the magnetic field variation for receiving guided waves. The experimental results show that the transducer with the corresponding inspection system could be applied to detect the broken wires in the free length and in the anchorage zone of bridge cables.

A Magnetic Flux Leakage and Magnetostrictive Guided Wave Hybrid Transducer for Detecting Bridge Cables

PubMed Central

Xu, Jiang; Wu, Xinjun; Cheng, Cheng; Ben, Anran

2012-01-01

Condition assessment of cables has gained considerable attention for the bridge safety. A magnetic flux leakage and magnetostrictive guided wave hybrid transducer is provided to inspect bridge cables. The similarities and differences between the two methods are investigated. The hybrid transducer for bridge cables consists of an aluminum framework, climbing modules, embedded magnetizers and a ribbon coil. The static axial magnetic field provided by the magnetizers meets the needs of the magnetic flux leakage testing and the magnetostrictive guided wave testing. The magnetizers also provide the attraction for the climbing modules. In the magnetic flux leakage testing for the free length of cable, the coil induces the axial leakage magnetic field. In the magnetostrictive guided wave testing for the anchorage zone, the coil provides a pulse high power variational magnetic field for generating guided waves; the coil induces the magnetic field variation for receiving guided waves. The experimental results show that the transducer with the corresponding inspection system could be applied to detect the broken wires in the free length and in the anchorage zone of bridge cables. PMID:22368483

Photospheric magnetic fields

NASA Technical Reports Server (NTRS)

Howard, R.

1972-01-01

Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

Eb&D: A new clustering approach for signed social networks based on both edge-betweenness centrality and density of subgraphs

NASA Astrophysics Data System (ADS)

Qi, Xingqin; Song, Huimin; Wu, Jianliang; Fuller, Edgar; Luo, Rong; Zhang, Cun-Quan

2017-09-01

Clustering algorithms for unsigned social networks which have only positive edges have been studied intensively. However, when a network has like/dislike, love/hate, respect/disrespect, or trust/distrust relationships, unsigned social networks with only positive edges are inadequate. Thus we model such kind of networks as signed networks which can have both negative and positive edges. Detecting the cluster structures of signed networks is much harder than for unsigned networks, because it not only requires that positive edges within clusters are as many as possible, but also requires that negative edges between clusters are as many as possible. Currently, we have few clustering algorithms for signed networks, and most of them requires the number of final clusters as an input while it is actually hard to predict beforehand. In this paper, we will propose a novel clustering algorithm called Eb &D for signed networks, where both the betweenness of edges and the density of subgraphs are used to detect cluster structures. A hierarchically nested system will be constructed to illustrate the inclusion relationships of clusters. To show the validity and efficiency of Eb &D, we test it on several classical social networks and also hundreds of synthetic data sets, and all obtain better results compared with other methods. The biggest advantage of Eb &D compared with other methods is that the number of clusters do not need to be known prior.

Note: An approach to 1000 T using the electro-magnetic flux compression.

PubMed

Nakamura, D; Sawabe, H; Takeyama, S

2018-01-01

The maximum magnetic field obtained by the electro-magnetic flux compression technique was investigated with respect to the initial seed magnetic field. It was found that the reduction in the seed magnetic field from 3.8 T to 3.0 T led to a substantial increase in the final peak magnetic field. The optical Faraday rotation method with a minimal size probe evades disturbances from electromagnetic noise and shockwave effects to detect such final peak fields in a reduced space of an inner wall of the imploding liner. The Faraday rotation signal recorded the maximum magnetic field increased significantly to the highest magnetic field of 985 T approaching 1000 T, ever achieved by the electro-magnetic flux compression technique as an indoor experiment.

A miniaturized human-motion energy harvester using flux-guided magnet stacks

NASA Astrophysics Data System (ADS)

Halim, M. A.; Park, J. Y.

2016-11-01

We present a miniaturized electromagnetic energy harvester (EMEH) using two flux-guided magnet stacks to harvest energy from human-generated vibration such as handshaking. Each flux-guided magnet stack increases (40%) the magnetic flux density by guiding the flux lines through a soft magnetic material. The EMEH has been designed to up-convert the applied human-motion vibration to a high-frequency oscillation by mechanical impact of a spring-less structure. The high-frequency oscillator consists of the analyzed 2-magnet stack and a customized helical compression spring. A standard AAA battery sized prototype (3.9 cm3) can generate maximum 203 μW average power from human hand-shaking vibration. It has a maximum average power density of 52 μWcm-3 which is significantly higher than the current state-of-the-art devices. A 6-stage multiplier and rectifier circuit interfaces the harvester with a wearable electronic load (wrist watch) to demonstrate its capability of powering small- scale electronic systems from human-generated vibration.

Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

NASA Technical Reports Server (NTRS)

Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

2003-01-01

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

Laboratory Evidence That Line-Tied Toroidal Magnetic Fields Can Suppress Loss-of-Equilibrium Flux Rope Eruptions in the Solar Corona

NASA Astrophysics Data System (ADS)

Myers, C. E.; Yamada, M.; Belova, E.; Ji, H.; Yoo, J.; Fox, W. R., II; Jara-Almonte, J.

2014-12-01

Loss-of-equilibrium mechanisms such as the ideal torus instability [Kliem & Török, Phys. Rev. Lett. 96, 255002 (2006)] are predicted to drive arched flux ropes in the solar corona to erupt. In recent line-tied flux rope experiments conducted in the Magnetic Reconnection Experiment (MRX), however, we find that quasi-statically driven flux ropes remain confined well beyond the predicted torus instability threshold. In order to understand this behavior, in situ measurements from a 300 channel 2D magnetic probe array are used to comprehensively analyze the force balance between the external (potential) and internal (plasma-generated) magnetic fields. We find that forces due to the line-tied toroidal magnetic field, which are not included in the basic torus instability theory, can play a major role in preventing eruptions. The dependence of these toroidal magnetic forces on various potential field and flux rope parameters will be discussed. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

Equilibrium features and eruptive instabilities in laboratory magnetic flux rope plasmas

NASA Astrophysics Data System (ADS)

Myers, Clayton E; Yamada, Masaaki; Belova, Elena V; Ji, Hantao; Yoo, Jongsoo; Fox, William

2014-06-01

One avenue for connecting laboratory and solar plasma studies is to carry out laboratory plasma experiments that serve as a well-diagnosed model for specific solar phenomena. In this paper, we present the latest results from one such laboratory experiment that is designed to address ideal instabilities that drive flux rope eruptions in the solar corona. The experiment, which utilizes the existing Magnetic Reconnection Experiment (MRX) at Princeton Plasma Physics Laboratory, generates a quasi-statically driven line-tied magnetic flux rope in a solar-relevant potential field arcade. The parameters of the potential field arcade (e.g., its magnitude, orientation, and vertical profile) are systematically scanned in order to study their influence on the evolution and possible eruption of the line-tied flux rope. Each flux rope discharge is diagnosed using a combination of fast visible light cameras and an in situ 2D magnetic probe array that measures all three components of the magnetic field over a large cross-section of the plasma. In this paper, we present the first results obtained from this new 2D magnetic probe array. With regard to the flux rope equilibrium, non-potential features such as the formation of a characteristic sigmoid shape and the generation of core toroidal field within the flux rope are studied in detail. With regard to instabilities, the onset and evolution of two key eruptive instabilities—the kink and torus instabilities—are quantitatively assessed as a function of the potential field arcade parameters and the amount of magnetic energy stored in the flux rope.This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

Skin-layer of the eruptive magnetic flux rope in large solar flares

NASA Astrophysics Data System (ADS)

Kichigin, G. N.; Miroshnichenko, L. I.; Sidorov, V. I.; Yazev, S. A.

2016-07-01

The analysis of observations of large solar flares made it possible to propose a hypothesis on existence of a skin-layer in magnetic flux ropes of coronal mass ejections. On the assumption that the Bohm coefficient determines the diffusion of magnetic field, an estimate of the skin-layer thickness of ~106 cm is obtained. According to the hypothesis, the electric field of ~0.01-0.1 V/cm, having the nonzero component along the magnetic field of flux rope, arises for ~5 min in the surface layer of the eruptive flux rope during its ejection into the upper corona. The particle acceleration by the electric field to the energies of ~100 MeV/nucleon in the skin-layer of the flux rope leads to their precipitation along field lines to footpoints of the flux rope. The skin-layer presence induces helical or oval chromospheric emission at the ends of flare ribbons. The emission may be accompanied by hard X-ray radiation and by the production of gamma-ray line at the energy of 2.223 MeV (neutron capture line in the photosphere). The magnetic reconnection in the corona leads to a shift of the skin-layer of flux rope across the magnetic field. The area of precipitation of accelerated particles at the flux-rope footpoints expands in this case from the inside outward. This effect is traced in the chromosphere and in the transient region as the expanding helical emission structures. If the emission extends to the spot, a certain fraction of accelerated particles may be reflected from the magnetic barrier (in the magnetic field of the spot). In the case of exit into the interplanetary space, these particles may be recorded in the Earth's orbit as solar proton events.

Characteristics of the spatial structure of Martian magnetic flux ropes recovered by the Grad-Shafranov reconstruction technique

NASA Astrophysics Data System (ADS)

Hara, T.; Seki, K.; Hasegawa, H.; Brain, D. A.; Matsunaga, K.; Saito, M. H.

2013-12-01

Mars is a unique planet because it locally possesses strong crustal magnetic fields mainly located in the southern hemisphere [e.g., Acuna et al., 1999]. The Martian electromagnetic environment can thus become highly complicated and variable, since the interplanetary magnetic field embedded in the solar wind interacts with the Martian crustal magnetic fields. Whereas it is known that the Martian upper atmosphere is escaping to interplanetary space due to the interaction with the solar wind [e.g., Lundin et al., 1989; Barabash et al., 2007], the contribution of crustal magnetic fields to atmospheric escape from Mars has not yet been well understood. Flux ropes are characteristic magnetic field structures seen throughout the solar system, e.g., at the Sun, in the interplanetary space, and at the terrestrial magnetosphere. Flux ropes are also observed at planets such as at Venus and Mars [e.g., Russell and Elphic, 1979; Vignes et al., 2004], which do not possess a global intrinsic magnetic field. Brain et al. [2010] found a large-scale isolated magnetic flux rope filled with Martian atmospheric plasma located downstream from the crustal magnetic fields with respect to the solar wind flow based on the Mars Global Surveyor (MGS) measurements. They suggested that the magnetic flux rope could be intermittently detached from Mars, and remove significant amounts of atmosphere away from Mars. They proposed that this process might occur frequently and account for as much as 10% of the total present-day ion escape from Mars. However, this estimation of the ion escape rate is somewhat ambiguous, because it is difficult to infer the spatial structure of them from the single spacecraft data. We here investigated characteristics of the Martian magnetic flux ropes based on the Grad-Shafranov (GS) reconstruction technique using the MGS magnetic field data. This technique is capable of recovering the two-dimensional spatial structure of the magnetic flux ropes from single spacecraft data [e.g., Hu and Sunnerup, 2002]. The resultant structure allows us to provide a reliable observational restriction on the spatial scales of magnetic flux ropes. We applied the GS reconstruction technique to 135 obvious magnetic flux rope events observed by MGS. As a result, their spatial structures were successfully recovered for 70 events. The reconstruction results indicated that magnetic flux rope axes are mostly oriented horizontally with respect to the Martian surface. We demonstrated that the events, which have solar zenith angle larger than 75 deg and duration longer than 240 sec, are mostly in the region where the upstream crustal magnetic field strength is larger than the other events. Using the shape and size of the flux ropes obtained from the GS reconstruction technique, we are able to calculate lower limits on their volume and the potential ion escape rates. The volumes can vary by factors of 2--3 orders of magnitude. Ion escape rates via the flux ropes based on the GS reconstruction technique turn out to attain to the order of 10^22 -- 10^23 ion/sec. This result could be comparable to the global ion escape rate obtained from the ion mass analyzer onboard the Mars Express orbiter at solar minimum [e.g., Barabash et al., 2007].

Escape of magnetic toroids from the Sun

NASA Technical Reports Server (NTRS)

Bieber, John W.; Rust, David M.

1995-01-01

Analysis of heliospheric magnetic fields at 1 AU shows that 10(exp 24) Mx of net azimuthal flux escapes from the Sun per solar cycle. This rate is consistent with rates derived from other indicators of flux escape, including coronal mass ejections and filament eruptions. The toroidal flux escape rate is compared with the apparent rate of flux emergence at the solar surface, and it is concluded that escaping toroids will remove at least 20% of the emerging flux, and may remove as much as 100% of emerging flux if multiple eruptions occur on the toroids. The data imply that flux escapes the Sun with an efficiency far exceeding Parker's upper limit estimate of 3%. Toroidal flux escape is almost certainly the source of the observed overwinding of the interplanetary magnetic field spiral. Two mechanisms to facilitate net flux escape are discussed: helicity charging to push open the fields and flux transport with reconnection to close them off. We estimate the Sun will shed approximately 2 x 10(exp 45) of magnetic helicity per solar cycle, leading to a mean helicity density of 100 Mx(exp 2)cm(exp -3) at 1 AU, which agrees well with observations.

Particle acceleration in relativistic magnetic flux-merging events

NASA Astrophysics Data System (ADS)

Lyutikov, Maxim; Sironi, Lorenzo; Komissarov, Serguei S.; Porth, Oliver

2017-12-01

Using analytical and numerical methods (fluid and particle-in-cell simulations) we study a number of model problems involving merger of magnetic flux tubes in relativistic magnetically dominated plasma. Mergers of current-carrying flux tubes (exemplified by the two-dimensional `ABC' structures) and zero-total-current magnetic flux tubes are considered. In all cases regimes of spontaneous and driven evolution are investigated. We identify two stages of particle acceleration during flux mergers: (i) fast explosive prompt X-point collapse and (ii) ensuing island merger. The fastest acceleration occurs during the initial catastrophic X-point collapse, with the reconnection electric field of the order of the magnetic field. During the X-point collapse, particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization . For plasma magnetization 2$ the spectrum power-law index is 2$ ; in this case the maximal energy depends linearly on the size of the reconnecting islands. For higher magnetization, 2$ , the spectra are hard, , yet the maximal energy \\text{max}$ can still exceed the average magnetic energy per particle, , by orders of magnitude (if is not too close to unity). The X-point collapse stage is followed by magnetic island merger that dissipates a large fraction of the initial magnetic energy in a regime of forced magnetic reconnection, further accelerating the particles, but proceeds at a slower reconnection rate.

Remagnetization effects due to lateral displacement above a PMG on bulk HTS magnet

NASA Astrophysics Data System (ADS)

Liu, W.; Wang, J. S.; Ma, G. T.; Zheng, J.; Ren, J. F.; Li, L. L.; Yang, X. F.; Ye, C. Q.; Wang, S. Y.

2012-12-01

For a high-Tc superconducting (HTS) maglev system with large force requirements, the use of magnetized bulk high-Tc superconductor magnets (MBSCMs) is a good candidate because of its strong flux pinning ability and corresponding high trapped flux. Different from the rare-earth permanent magnet (PM), the trapped flux of a MBSCM is sustained by the supercurrent produced by a magnetizing process, so the trapped flux is sensitive to variations of the supercurrent. The lateral displacement of a MBSCM above a PM guideway (PMG) will provide disturbance of the applied field and then alter the supercurrent as a process of remagnetization. Different magnetization histories will bring different remagnetization characteristics and consequently diverse levitation performances for a MBSCM during the lateral displacements. When the MBSCMs are applied into the HTS maglev system, the influence of lateral displacements on levitation performance should be taken into consideration. This article investigates the remagnetization characteristics of a MBSCM when it is subject to the lateral displacements above a PMG with different trapped magnetic flux and opposite magnetization polarities. Relevant analyses about the internal supercurrent configuration based on the critical state model are also included to better understand the remagnetization characteristic of a MBSCM.

Critical Magnetic Field Strengths for Unipolar Solar Coronal Plumes In Quiet Regions and Coronal Holes?

NASA Technical Reports Server (NTRS)

Avallone, Ellis; Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.; Winebarger, Amy

2017-01-01

Coronal plumes are bright magnetic funnels that are found in quiet regions and coronal holes that extend high into the solar corona whose lifetimes can last from hours to days. The heating processes that make plumes bright involve the magnetic field at the base of the plume, but their intricacies remain mysterious. Raouafi et al. (2014) infer from observation that plume heating is a consequence of magnetic reconnection at the base, whereas Wang et al. (2016) infer that plume heating is a result of convergence of the magnetic flux at the plume's base, or base flux. Both papers suggest that the base flux in their plumes is of mixed polarity, but do not quantitatively measure the base flux or consider whether a critical magnetic field strength is required for plume production. To investigate the magnetic origins of plume heating, we track plume luminosity in the 171 Å wavelength as well as the abundance and strength of the base flux over the lifetimes of six unipolar coronal plumes. Of these, three are in coronal holes and three are in quiet regions. For this sample, we find that plume heating is triggered when convergence of the base flux surpasses a field strength of approximately 300 - 500 Gauss, and that the luminosity of both quiet region and coronal hole plumes respond similarly to the strength of the magnetic field in the base.

Numerical study of compressible magnetoconvection with an open transitional boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanami, H.; Tajima, T.

1990-08-01

We study by computer simulation nonlinear evolution of magnetoconvection in a system with a dynamical open boundary between the convection region and corona of the sun. We study a model in which the fluid is subject to the vertical gravitation, magnetohydrodynamics (MHD), and high stratification, through an MHD code with the MacCormack-Donner cell hybrid scheme in order to well represent convective phenomena. Initially the vertical fluid flux penetrates from the convectively unstable zone at the bottom into the upper diffuse atmosphere. As the instability develops, the magnetic fields are twisted by the convection motion and the folding magnetic fields ismore » observed. When the magnetic pressure is comparable to the thermal pressure in the upper layer of convective zone, strong flux expulsion from the convective cell interior toward the cell boundary appears. Under appropriate conditions our simulation exhibits no shock formation incurred by the fluid convected to the photosphere, in contrast to earlier works with box boundaries. The magnetic field patterns observed are those of concentrated magnetic flux tubes, accumulation of dynamo flux near the bottom boundary, pinched flux near the downdraft region, and the surface movement of magnetic flux toward the downdraft region. Many of these computationally observed features are reminiscent of solar observations of the fluid and magnetic structures of their motions.« less

Intrinsic Magnetic Flux of the Electron's Orbital and Spin Motion

NASA Astrophysics Data System (ADS)

Wan, K. K.; Saglam, M.

2006-06-01

In analogy with the fact that there are magnetic moments associated respectively with the electron's orbital and spin motion in an atom we present several analyses on a proposal to introduce a concept of intrinsic magnetic flux associated with the electron's orbital and spin motion. It would be interesting to test or to demonstrate Faraday's and Lenz's laws of electromagnetic induction arising directly from the flux change due to transition of states in an atom and to examine applications of this concept of intrinsic flux.

Energy release and transfer in guide field reconnection

NASA Astrophysics Data System (ADS)

Birn, J.; Hesse, M.

2010-01-01

Properties of energy release and transfer by magnetic reconnection in the presence of a guide field are investigated on the basis of 2.5-dimensional magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations. Two initial configurations are considered: a plane current sheet with a uniform guide field of 80% of the reconnecting magnetic field component and a force-free current sheet in which the magnetic field strength is constant but the field direction rotates by 180° through the current sheet. The onset of reconnection is stimulated by localized, temporally limited compression. Both MHD and PIC simulations consistently show that the outgoing energy fluxes are dominated by (redirected) Poynting flux and enthalpy flux, whereas bulk kinetic energy flux and heat flux (in the PIC simulation) are small. The Poynting flux is mainly associated with the magnetic energy of the guide field which is carried from inflow to outflow without much alteration. The conversion of annihilated magnetic energy to enthalpy flux (that is, thermal energy) stems mainly from the fact that the outflow occurs into a closed field region governed by approximate force balance between Lorentz and pressure gradient forces. Therefore, the energy converted from magnetic to kinetic energy by Lorentz force acceleration becomes immediately transferred to thermal energy by the work done by the pressure gradient force. Strong similarities between late stages of MHD and PIC simulations result from the fact that conservation of mass and entropy content and footpoint displacement of magnetic flux tubes, imposed in MHD, are also approximately satisfied in the PIC simulations.

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

NASA Astrophysics Data System (ADS)

Hubert, Benoit; Gérard, Jean-Claude; Milan, Steve E.; Cowley, Stanley W. H.

2017-03-01

We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average ˜ 0.745 GWb, standard deviation ˜ 0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of ˜ 450 km s-1. We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals.

Multi-wavelength Observations and Modeling of Solar Flares: Magnetic Structures

NASA Astrophysics Data System (ADS)

Su, Y.

2017-12-01

We present a review of our recent investigations on multi-wavelength observations and magnetic field modeling of solar flares. High-resolution observations taken by NVST and BBSO/NST reveal unprecedented fine structures of the flaring regions. Observations by SDO, IRIS, and GOES provide the complementary information. The magnetic field models are constructed using either non-linear force free field extrapolations or flux rope insertion method. Our studies have shown that the flaring regions often consist of double or multiple flux ropes, which often exist at different heights. The fine flare ribbon structures may be due to the magnetic reconnection in the complex quasi separatrix layers. The magnetic field modeling of several large flares suggests that the so called hot-channel structure is corresponding to the erupting flux rope above the X-point in a magnetic configuration with Hyperbolic Flux Tube.

First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

DOE PAGES

Rosenberg, M. J.; Li, C. K.; Fox, W.; ...

2015-04-08

Novel experiments to study the strongly-driven collision of parallel magnetic fields in β~10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell (PIC) simulations predict a stronger flux compressionmore » and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.« less

Investigation of measurement method of saturation magnetization of iron core material using electromagnet

NASA Astrophysics Data System (ADS)

Shibataki, Takuya; Takahashi, Yasuhito; Fujiwara, Koji

2018-04-01

This paper discusses a measurement method for saturation magnetizations of iron core materials using an electromagnet, which can apply an extremely large magnetic field strength to a specimen. It is said that electrical steel sheets are completely saturated at such a large magnetic field strength over about 100 kA/m. The saturation magnetization can be obtained by assuming that the completely saturated specimen shows a linear change of the flux density with the magnetic field strength because the saturation magnetization is constant. In order to accurately evaluate the flux density in the specimen, an air flux between the specimen and a winding of B-coil for detecting the flux density is compensated by utilizing an ideal condition that the incremental permeability of saturated specimen is equal to the permeability of vacuum. An error of magnetic field strength caused by setting a sensor does not affect the measurement accuracy of saturation magnetization. The error is conveniently cancelled because the saturation magnetization is a function of a ratio of the magnetic field strength to its increment. It may be concluded that the saturation magnetization can be easily measured with high accuracy by using the proposed method.

Magnetic flux studies in horizontally cooled elliptical superconducting cavities

DOE PAGES

Martinello, M.; Checchin, M.; Grassellino, A.; ...

2015-07-29

Previous studies on magnetic flux expulsion as a function of cooldown procedures for elliptical superconducting radio frequency (SRF) niobium cavities showed that when the cavity beam axis is placed parallel to the helium cooling flow and sufficiently large thermal gradients are achieved, all magnetic flux could be expelled and very low residual resistance could be achieved. In this paper, we investigate flux trapping for the case of resonators positioned perpendicularly to the helium cooling flow, which is more representative of how SRF cavities are cooled in accelerators and for different directions of the applied magnetic field surrounding the resonator. Wemore » show that different field components have a different impact on the surface resistance, and several parameters have to be considered to fully understand the flux dynamics. A newly discovered phenomenon of concentration of flux lines at the cavity top leading to temperature rise at the cavity equator is presented.« less

Pre-eruptive Magnetic Reconnection within a Multi-flux-rope System in the Solar Corona

NASA Astrophysics Data System (ADS)

Awasthi, Arun Kumar; Liu, Rui; Wang, Haimin; Wang, Yuming; Shen, Chenglong

2018-04-01

The solar corona is frequently disrupted by coronal mass ejections (CMEs), whose core structure is believed to be a flux rope made of helical magnetic field. This has become a “standard” picture; though, it remains elusive how the flux rope forms and evolves toward eruption. While one-third of the ejecta passing through spacecraft demonstrate a flux-rope structure, the rest have complex magnetic fields. Are they originating from a coherent flux rope, too? Here we investigate the source region of a complex ejecta, focusing on a flare precursor with definitive signatures of magnetic reconnection, i.e., nonthermal electrons, flaring plasma, and bidirectional outflowing blobs. Aided by nonlinear force-free field modeling, we conclude that the reconnection occurs within a system of multiple braided flux ropes with different degrees of coherency. The observation signifies the importance of internal structure and dynamics in understanding CMEs and in predicting their impacts on Earth.

Three-dimensional forward solver and its performance analysis for magnetic resonance electrical impedance tomography (MREIT) using recessed electrodes.

PubMed

Lee, Byung Il; Oh, Suk Hoon; Woo, Eung Je; Lee, Soo Yeol; Cho, Min Hyoung; Kwon, Ohin; Seo, Jin Keun; Lee, June-Yub; Baek, Woon Sik

2003-07-07

In magnetic resonance electrical impedance tomography (MREIT), we try to reconstruct a cross-sectional resistivity (or conductivity) image of a subject. When we inject a current through surface electrodes, it generates a magnetic field. Using a magnetic resonance imaging (MRI) scanner, we can obtain the induced magnetic flux density from MR phase images of the subject. We use recessed electrodes to avoid undesirable artefacts near electrodes in measuring magnetic flux densities. An MREIT image reconstruction algorithm produces cross-sectional resistivity images utilizing the measured internal magnetic flux density in addition to boundary voltage data. In order to develop such an image reconstruction algorithm, we need a three-dimensional forward solver. Given injection currents as boundary conditions, the forward solver described in this paper computes voltage and current density distributions using the finite element method (FEM). Then, it calculates the magnetic flux density within the subject using the Biot-Savart law and FEM. The performance of the forward solver is analysed and found to be enough for use in MREIT for resistivity image reconstructions and also experimental designs and validations. The forward solver may find other applications where one needs to compute voltage, current density and magnetic flux density distributions all within a volume conductor.

Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

NASA Astrophysics Data System (ADS)

Lousberg, Gregory P.; Fagnard, Jean-François; Noudem, Jacques G.; Ausloos, Marcel; Vanderheyden, Benoit; Vanderbemden, Philippe

2009-04-01

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30 to 130 mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.

The Role of Kinetic Alfven Waves in Plasma Transport in an Ion-scale Flux Rope

NASA Astrophysics Data System (ADS)

Tang, B.; Li, W.; Wang, C.; Dai, L.

2017-12-01

Magnetic flux ropes, if generated by multiply X-line reconnections, would be born as a crater type one, meaning the plasma density within is relatively high. They will then evolve into typical flux ropes as plasma are transported away along the magnetic field lines [Zhang et al., 2010]. In this study, we report an ion-scale flux rope observed by MMS on November 28, 2016, which is accompanied by strong kinetic Alfven waves (KAW). The related wave parallel electric field can effectively accelerate electrons inside the flux rope by Landau resonance, resulting into a significant decrease of the electron at 90° pitch angle. The change of electron pitch angle distribution would cause the rapid plasma transport along the magnetic field lines, and help the flux rope evolve into a strong magnetic core in a short time. This wave-particle interaction would be a candidate mechanism to explain the rareness of crater flux ropes in reality.

Siphon flows in isolated magnetic flux tubes. II - Adiabatic flows

NASA Technical Reports Server (NTRS)

Montesinos, Benjamin; Thomas, John H.

1989-01-01

This paper extends the study of steady siphon flows in isolated magnetic flux tubes surrounded by field-free gas to the case of adiabatic flows. The basic equations governing steady adiabatic siphon flows in a thin, isolated magnetic flux tube are summarized, and qualitative features of adiabatic flows in elevated, arched flux tubes are discussed. The equations are then cast in nondimensional form and the results of numerical computations of adiabatic siphon flows in arched flux tubes are presented along with comparisons between isothermal and adiabatic flows. The effects of making the interior of the flux tube hotter or colder than the surrounding atmosphere at the upstream footpoint of the arch is considered. In this case, is it found that the adiabatic flows are qualitatively similar to the isothermal flows, with adiabatic cooling producing quantitative differences. Critical flows can produce a bulge point in the rising part of the arch and a concentration of magnetic flux above the bulge point.

A high magnetic Reynolds number dynamo

NASA Technical Reports Server (NTRS)

Perkins, F. W.; Zweibel, E. G.

1987-01-01

A boundary-layer solution to a high magnetic Reynolds number R periodic dynamo model shows that: (1) flux expulsion forces the magnetic field into flux sheets; (2) the principal contribution to the alpha effect arises from regions of flow stagnation along a flux sheet; and (3) the alpha effect scales as R exp-1/2. Arguments for these effects persisting in turbulent dynamos are given.

Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bodo, G.; Rossi, P.; Cattaneo, F.

We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge—the winding gauge—that provides a natural interpretation in terms of the average winding number of pairwise field lines. We usemore » this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.« less

Modelling total solar irradiance since 1878 from simulated magnetograms

NASA Astrophysics Data System (ADS)

Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.

2014-10-01

Aims: We present a new model of total solar irradiance (TSI) based on magnetograms simulated with a surface flux transport model (SFTM) and the Spectral And Total Irradiance REconstructions (SATIRE) model. Our model provides daily maps of the distribution of the photospheric field and the TSI starting from 1878. Methods: The modelling is done in two main steps. We first calculate the magnetic flux on the solar surface emerging in active and ephemeral regions. The evolution of the magnetic flux in active regions (sunspots and faculae) is computed using a surface flux transport model fed with the observed record of sunspot group areas and positions. The magnetic flux in ephemeral regions is treated separately using the concept of overlapping cycles. We then use a version of the SATIRE model to compute the TSI. The area coverage and the distribution of different magnetic features as a function of time, which are required by SATIRE, are extracted from the simulated magnetograms and the modelled ephemeral region magnetic flux. Previously computed intensity spectra of the various types of magnetic features are employed. Results: Our model reproduces the PMOD composite of TSI measurements starting from 1978 at daily and rotational timescales more accurately than the previous version of the SATIRE model computing TSI over this period of time. The simulated magnetograms provide a more realistic representation of the evolution of the magnetic field on the photosphere and also allow us to make use of information on the spatial distribution of the magnetic fields before the times when observed magnetograms were available. We find that the secular increase in TSI since 1878 is fairly stable to modifications of the treatment of the ephemeral region magnetic flux.

Model of driven and decaying magnetic turbulence in a cylinder.

PubMed

Kemel, Koen; Brandenburg, Axel; Ji, Hantao

2011-11-01

Using mean-field theory, we compute the evolution of the magnetic field in a cylinder with outer perfectly conducting boundaries and imposed axial magnetic and electric fields. The thus injected magnetic helicity in the system can be redistributed by magnetic helicity fluxes down the gradient of the local current helicity of the small-scale magnetic field. A weak reversal of the axial magnetic field is found to be a consequence of the magnetic helicity flux in the system. Such fluxes are known to alleviate so-called catastrophic quenching of the α effect in astrophysical applications. A stronger field reversal can be obtained if there is also a significant kinetic α effect. Application to the reversed field pinch in plasma confinement devices is discussed.

Development of energy-harvesting system using deformation of magnetic elastomer

NASA Astrophysics Data System (ADS)

Shinoda, Hayato; Tsumori, Fujio

2018-06-01

In this paper, we propose a power generation method using the deformation of a magnetic elastomer for vibration energy harvesting. The magnetic flux lines in the structure of the magnetic elastomer could be markedly changed if the properly designed structure was expanded and contracted in a static magnetic field. We set a coil on the magnetic elastomer to generate electricity by capturing this change in magnetic flux flow. We fabricated a centimeter-scale device and demonstrated that it generated 10.5 mV of maximum voltage by 10 Hz vibration. We also simulated the change in the magnetic flux flow using finite element analysis, and compared the result with the experimental data. Furthermore, we evaluated the power generation of a miniaturized device.

Left-Turn Bays

DOT National Transportation Integrated Search

1996-05-01

The topic of left-turn bays (left-turn lanes) involves the following three issues: 1.) Warrants; 2.) Bay Length and 3.) Design Details. This discussion paper deals with warrants and bay length -- including queue storage at signalized and unsignalized...

MMS Examination of FTEs at the Earth's Subsolar Magnetopause

NASA Astrophysics Data System (ADS)

Akhavan-Tafti, M.; Slavin, J. A.; Le, G.; Eastwood, J. P.; Strangeway, R. J.; Russell, C. T.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Giles, B. L.; Gershman, D. J.; Burch, J. L.

2018-02-01

Determining the magnetic field structure, electric currents, and plasma distributions within flux transfer event (FTE)-type flux ropes is critical to the understanding of their origin, evolution, and dynamics. Here the Magnetospheric Multiscale mission's high-resolution magnetic field and plasma measurements are used to identify FTEs in the vicinity of the subsolar magnetopause. The constant-α flux rope model is used to identify quasi-force free flux ropes and to infer the size, the core magnetic field strength, the magnetic flux content, and the spacecraft trajectories through these structures. Our statistical analysis determines a mean diameter of 1,700 ± 400 km ( 30 ± 9 di) and an average magnetic flux content of 100 ± 30 kWb for the quasi-force free FTEs at the Earth's subsolar magnetopause which are smaller than values reported by Cluster at high latitudes. These observed nonlinear size and magnetic flux content distributions of FTEs appear consistent with the plasmoid instability theory, which relies on the merging of neighboring, small-scale FTEs to generate larger structures. The ratio of the perpendicular to parallel components of current density, RJ, indicates that our FTEs are magnetically force-free, defined as RJ < 1, in their core regions (<0.6 Rflux rope). Plasma density is shown to be larger in smaller, newly formed FTEs and dropping with increasing FTE size. It is also shown that parallel ion velocity dominates inside FTEs with largest plasma density. Field-aligned flow facilitates the evacuation of plasma inside newly formed FTEs, while their core magnetic field strengthens with increasing FTE size.

How Well Can the Observed Flux Ropes in the Solar Wind be Fitted by a Uniform-twist Flux Rope Model?

NASA Astrophysics Data System (ADS)

Wang, Y.

2015-12-01

In the solar wind, flux ropes, e.g., magnetic clouds (MCs), are a frequently observational phenomenon. Their magnetic field configuration or the way that the field lines wind around the flux rope axis is one of the most important information to understand the formation and evolution of the observed flux ropes. Most MCs are believed to be in the force-free state, and widely modeled by the Lundquist force-free solution, in which the twist of the field line increases from zero at the axis to infinity at the boundary. However, Lundquist solution is not the only form of a force-free magnetic field. Some studies based on suprathermal electron observations and models have shown that MCs may carry magnetic field lines more likely to be uniformly twisted. The nonlinear force-free field extrapolation of solar magnetic field also suggests that the field lines of a flux rope twist limitedly. In this study, we have developed a velocity-modified uniform-twist force-free flux rope model, and fit observed MCs with this model. By using this approach, we test how well the observed MCs can be fitted into a uniform-twist flux rope. Some interesting results will be given in this presentation.

Magnetic moment of single layer graphene rings

NASA Astrophysics Data System (ADS)

Margulis, V. A.; Karpunin, V. V.; Mironova, K. I.

2018-01-01

Magnetic moment of single layer graphene rings is investigated. An analytical expression for the magnetic moment as a function of the magnetic field flux through the one-dimensional quantum rings is obtained. This expression has the oscillation character. The oscillation period is equal to one flux quanta.

A dynamic magnetic tension force as the cause of failed solar eruptions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myers, Clayton E.; Yamada, Masaaki; Ji, Hantao

Coronal mass ejections are solar eruptions driven by a sudden release of magnetic energy stored in the Sun's corona. In many cases, this magnetic energy is stored in long-lived, arched structures called magnetic flux ropes. When a flux rope destabilizes, it can either erupt and produce a coronal mass ejection or fail and collapse back towards the Sun. The prevailing belief is that the outcome of a given event is determined by a magnetohydrodynamic force imbalance called the torus instability. This belief is challenged, however, by observations indicating that torus-unstable flux ropes sometimes fail to erupt. This contradiction has notmore » yet been resolved because of a lack of coronal magnetic field measurements and the limitations of idealized numerical modelling. In this paper, we report the results of a laboratory experiment that reveal a previously unknown eruption criterion below which torus-unstable flux ropes fail to erupt. We find that such 'failed torus' events occur when the guide magnetic field (that is, the ambient field that runs toroidally along the flux rope) is strong enough to prevent the flux rope from kinking. Under these conditions, the guide field interacts with electric currents in the flux rope to produce a dynamic toroidal field tension force that halts the eruption. Lastly, this magnetic tension force is missing from existing eruption models, which is why such models cannot explain or predict failed torus events.« less

A dynamic magnetic tension force as the cause of failed solar eruptions

DOE PAGES

Myers, Clayton E.; Yamada, Masaaki; Ji, Hantao; ...

2015-12-23

Coronal mass ejections are solar eruptions driven by a sudden release of magnetic energy stored in the Sun's corona. In many cases, this magnetic energy is stored in long-lived, arched structures called magnetic flux ropes. When a flux rope destabilizes, it can either erupt and produce a coronal mass ejection or fail and collapse back towards the Sun. The prevailing belief is that the outcome of a given event is determined by a magnetohydrodynamic force imbalance called the torus instability. This belief is challenged, however, by observations indicating that torus-unstable flux ropes sometimes fail to erupt. This contradiction has notmore » yet been resolved because of a lack of coronal magnetic field measurements and the limitations of idealized numerical modelling. In this paper, we report the results of a laboratory experiment that reveal a previously unknown eruption criterion below which torus-unstable flux ropes fail to erupt. We find that such 'failed torus' events occur when the guide magnetic field (that is, the ambient field that runs toroidally along the flux rope) is strong enough to prevent the flux rope from kinking. Under these conditions, the guide field interacts with electric currents in the flux rope to produce a dynamic toroidal field tension force that halts the eruption. Lastly, this magnetic tension force is missing from existing eruption models, which is why such models cannot explain or predict failed torus events.« less

Flux Cancellation Leading to Solar Filament Eruptions

NASA Astrophysics Data System (ADS)

Popescu, R. M.; Panesar, N. K.; Sterling, A. C.; Moore, R. L.

2016-12-01

Solar filaments are strands of relatively cool, dense plasma magnetically suspended in the lower density hotter solar corona. They trace magnetic polarity inversion lines (PILs) in the photosphere below, and are supported against gravity at heights of up to 100 Mm above the chromosphere by the magnetic field in and around them. This field erupts when it is rendered unstable by either magnetic flux cancellation or emergence at or near the PIL. We have studied the evolution of photospheric magnetic flux leading to ten observed filament eruptions. Specifically, we look for gradual magnetic changes in the neighborhood of the PIL prior to and during eruption. We use Extreme Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA), and magnetograms from the Helioseismic and Magnetic Imager (HMI), both onboard the Solar Dynamics Observatory (SDO), to study filament eruptions and their photospheric magnetic fields. We examine whether flux cancellation or/and emergence leads to filament eruptions and find that continuous flux cancellation was present at the PIL for many hours prior to each eruption. We present two events in detail and find the following: (a) the pre-eruption filament-holding core field is highly sheared and appears in the shape of a sigmoid above the PIL; (b) at the start of the eruption the opposite arms of the sigmoid reconnect in the middle above the site of (tether-cutting) flux cancellation at the PIL; (c) the filaments first show a slow-rise, followed by a fast-rise as they erupt. We conclude that these two filament eruptions result from flux cancellation in the middle of the sheared field and are in agreement with the standard model for a CME/flare filament eruption from a closed bipolar magnetic field [flux cancellation (van Ballegooijen and Martens 1989 and Moore and Roumelrotis 1992) and runaway tether-cutting (Moore et. al 2001)].

Flux Cancellation Leading to CME Filament Eruptions

NASA Technical Reports Server (NTRS)

Popescu, Roxana M.; Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

2016-01-01

Solar filaments are strands of relatively cool, dense plasma magnetically suspended in the lower density hotter solar corona. They trace magnetic polarity inversion lines (PILs) in the photosphere below, and are supported against gravity at heights of up to approx.100 Mm above the chromosphere by the magnetic field in and around them. This field erupts when it is rendered unstable, often by magnetic flux cancellation or emergence at or near the PIL. We have studied the evolution of photospheric magnetic flux leading to ten observed filament eruptions. Specifically, we look for gradual magnetic changes in the neighborhood of the PIL prior to and during eruption. We use Extreme Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA), and magnetograms from the Helioseismic and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO), to study filament eruptions and their photospheric magnetic fields. We examine whether flux cancellation or/and emergence leads to filament eruptions. We find that continuous flux cancellation was present at the PIL for many hours prior to each eruption. We present two CME-producing eruptions in detail and find the following: (a) the pre-eruption filament-holding core field is highly sheared and appears in the shape of a sigmoid above the PIL; (b) at the start of the eruption the opposite arms of the sigmoid reconnect in the middle above the site of (tether-cutting) flux cancellation at the PIL; (c) the filaments first show a slow-rise, followed by a fast-rise as they erupt. We conclude that these two filament eruptions result from flux cancellation in the middle of the sheared field, and thereafter evolve in agreement with the standard model for a CME/flare filament eruption from a closed bipolar magnetic field [flux cancellation (van Ballegooijen and Martens 1989 and Moore and Roumelrotis 1992) and runaway tether-cutting (Moore et. al 2001)].

Powerful actuation of magnetized microtools by focused magnetic field for particle sorting in a chip.

PubMed

Yamanishi, Yoko; Sakuma, Shinya; Onda, Kazuhisa; Arai, Fumihito

2010-08-01

This paper describes a novel powerful noncontact actuation of a magnetically driven microtool (MMT), achieved by magnetization of the MMT and focusing of the magnetic field in a microfluidic chip for particle sorting. The following are the highlights of this study: (1) an MMT was successfully fabricated from a mixture of neodymium powder and polydimethylsiloxane; the MMT was magnetized such that it acted as an elastic micromagnet with a magnetic flux density that increased by about 100 times after magnetization, and (2) a pair of sharp magnetic needles was fabricated adjacent to a microchannel in a chip by electroplating, in order to focus the magnetic flux density generated by the electromagnetic coils below the biochip; these needles contribute to miniaturization of an actuation module that would enable the integration of multiple functions in the limited area of a chip. FEM analysis of the magnetic flux density around the MMT showed that the magnetic flux density in the setup with the magnetic needles was around 8 times better than that in the setup without the needles. By magnetization, the drive frequency of the MMT improved by about 10 times--from 18 Hz to 180 Hz. We successfully demonstrated the separation of copolymer beads of a particular size in a chip by image sensing.

Design of magnetic Circuit Simulation for Curing Device of Anisotropic MRE

NASA Astrophysics Data System (ADS)

Hapipi, N.; Ubaidillah; Mazlan, S. A.; Widodo, P. J.

2018-03-01

The strength of magnetic field during fabrication of magnetorheological elastomer (MRE) plays a crucial role in order to form a pre-structured MRE. So far, gaussmeter were used to determine the magnetic intensity subjected to the MRE during curing. However, the magnetic flux reading through that measurement considered less accurate. Therefore, a simulation should be done to figure out the magnetic flux concentration around the sample. This paper investigates the simulation of magnetic field distribution in a curing device used during curing stage of anisotropic magnetorheological elastomer (MRE). The target in designing the magnetic circuit is to ensure a sufficient and uniform magnetic field to all the MRE surfaces during the curing process. The magnetic circuit design for the curing device was performed using Finite Element Method Magnetic (FEMM) to examine the magnetic flux density distribution in the device. The material selection was first done instantaneously during a magnetic simulation process. Then, the experimental validation of simulation was performed by measuring and comparing the actual flux generated within the specimen type and the one from the FEMM simulation. İt apparent that the data from FEMM simulation shows an agreement with the actual measurement. Furthermore, the FEMM results showed that the magnetic design is able to provide sufficient and uniform magnetic field all over the surfaces of the MRE.

Statistical evolution of quiet-Sun small-scale magnetic features using Sunrise observations

NASA Astrophysics Data System (ADS)

Anusha, L. S.; Solanki, S. K.; Hirzberger, J.; Feller, A.

2017-02-01

The evolution of small magnetic features in quiet regions of the Sun provides a unique window for probing solar magneto-convection. Here we analyze small-scale magnetic features in the quiet Sun, using the high resolution, seeing-free observations from the Sunrise balloon borne solar observatory. Our aim is to understand the contribution of different physical processes, such as splitting, merging, emergence and cancellation of magnetic fields to the rearrangement, addition and removal of magnetic flux in the photosphere. We have employed a statistical approach for the analysis and the evolution studies are carried out using a feature-tracking technique. In this paper we provide a detailed description of the feature-tracking algorithm that we have newly developed and we present the results of a statistical study of several physical quantities. The results on the fractions of the flux in the emergence, appearance, splitting, merging, disappearance and cancellation qualitatively agrees with other recent studies. To summarize, the total flux gained in unipolar appearance is an order of magnitude larger than the total flux gained in emergence. On the other hand, the bipolar cancellation contributes nearly an equal amount to the loss of magnetic flux as unipolar disappearance. The total flux lost in cancellation is nearly six to eight times larger than the total flux gained in emergence. One big difference between our study and previous similar studies is that, thanks to the higher spatial resolution of Sunrise, we can track features with fluxes as low as 9 × 1014 Mx. This flux is nearly an order of magnitude lower than the smallest fluxes of the features tracked in the highest resolution previous studies based on Hinode data. The area and flux of the magnetic features follow power-law type distribution, while the lifetimes show either power-law or exponential type distribution depending on the exact definitions used to define various birth and death events. We have also statistically determined the evolution of the flux within the features in the course of their lifetime, finding that this evolution depends very strongly on the birth and death process that the features undergo.

Connecting the large- and the small-scale magnetic fields of solar-like stars

NASA Astrophysics Data System (ADS)

Lehmann, L. T.; Jardine, M. M.; Mackay, D. H.; Vidotto, A. A.

2018-05-01

A key question in understanding the observed magnetic field topologies of cool stars is the link between the small- and the large-scale magnetic field and the influence of the stellar parameters on the magnetic field topology. We examine various simulated stars to connect the small-scale with the observable large-scale field. The highly resolved 3D simulations we used couple a flux transport model with a non-potential coronal model using a magnetofrictional technique. The surface magnetic field of these simulations is decomposed into spherical harmonics which enables us to analyse the magnetic field topologies on a wide range of length scales and to filter the large-scale magnetic field for a direct comparison with the observations. We show that the large-scale field of the self-consistent simulations fits the observed solar-like stars and is mainly set up by the global dipolar field and the large-scale properties of the flux pattern, e.g. the averaged latitudinal position of the emerging small-scale field and its global polarity pattern. The stellar parameters flux emergence rate, differential rotation and meridional flow affect the large-scale magnetic field topology. An increased flux emergence rate increases the magnetic flux in all field components and an increased differential rotation increases the toroidal field fraction by decreasing the poloidal field. The meridional flow affects the distribution of the magnetic energy across the spherical harmonic modes.

Analysis of Magnetic Flux Rope Chains Embedded in Martian Current Sheets Using MAVEN Data

NASA Astrophysics Data System (ADS)

Bowers, C. F.; DiBraccio, G. A.; Brain, D.; Hara, T.; Gruesbeck, J.; Espley, J. R.; Connerney, J. E. P.; Halekas, J. S.

2017-12-01

The magnetotail of Mars is formed as the interplanetary magnetic field (IMF) drapes around the planet's conducting ionosphere and localized crustal magnetic fields. In this scenario, a cross-tail current sheet separates the sunward and anti-sunward tail lobes. This tail current sheet is a highly dynamic region where magnetic reconnection is able to occur between the oppositely oriented fields. Magnetic flux ropes, a by-product of magnetic reconnection in the tail or in the ionosphere characterized by their helical outer wraps and strong axial core field, are commonly observed in the Martian magnetotail. An initial study using Mars Global Surveyor measurements reported a chain of flux ropes in the tail. During this event, 3 flux ropes were observed during a single traversal of the tail current sheet with a duration of 4 minutes. Here, we perform a statistical survey of these chain-of-flux-rope events to characterize their occurrence in the tail current sheet using Mars Atmosphere and Volatile EvolutioN (MAVEN) data. We implement the well-established technique of Minimum Variance Analysis to confirm the helical structure of the flux ropes and also determine local current sheet orientation. Thorough visual examination of more than 1600 orbits has resulted in the identification of 784 tail current sheet traversals. We determine the current sheet thickness to be on the order of 100-1000 km. From these current sheet observations, a subset of 30 events include embedded chain of flux ropes within the current sheet structure. We find that 87% of these flux rope chain events are identified in the southern latitude regions of Mars, associated with crustal fields. Their location suggests that magnetic reconnection occurring near crustal fields may be the source of these flux ropes. These statistical measurements of both current sheets and associated flux rope chains provide information about the complex magnetospheric dynamics at Mars, and how these dynamics affect atmospheric loss to space.

Magnetohydrodynamic simulations of the ejection of a magnetic flux rope

NASA Astrophysics Data System (ADS)

Pagano, P.; Mackay, D. H.; Poedts, S.

2013-06-01

Context. Coronal mass ejections (CME's) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model. In this model, magnetic flux ropes form slowly over time periods of days to weeks. They then lose equilibrium and are ejected from the solar corona over a few hours. The contrasting time scales of formation and ejection pose a serious problem for numerical simulations. Aims: We simulate the whole life span of a flux rope from slow formation to rapid ejection and investigate whether magnetic flux ropes formed from a continuous magnetic field distribution, during a quasi-static evolution, can erupt to produce a CME. Methods: To model the full life span of magnetic flux ropes we couple two models. The global non-linear force-free field (GNLFFF) evolution model is used to follow the quasi-static formation of a flux rope. The MHD code ARMVAC is used to simulate the production of a CME through the loss of equilibrium and ejection of this flux rope. Results: We show that the two distinct models may be successfully coupled and that the flux rope is ejected out of our simulation box, where the outer boundary is placed at 2.5 R⊙. The plasma expelled during the flux rope ejection travels outward at a speed of 100 km s-1, which is consistent with the observed speed of CMEs in the low corona. Conclusions: Our work shows that flux ropes formed in the GNLFFF can lead to the ejection of a mass loaded magnetic flux rope in full MHD simulations. Coupling the two distinct models opens up a new avenue of research to investigate phenomena where different phases of their evolution occur on drastically different time scales. Movies are available in electronic form at http://www.aanda.org

Theoretical mechanisms for solar eruptions

NASA Astrophysics Data System (ADS)

Lin, Jun

This thesis presents new theoretical models of solar eruptions which are derived from older models that involve a loss of equilibrium of the Sun's coronal magnetic field. These models consist of a magnetic flux rope nested within an arcade of magnetic loop. Prior to an eruption, the flux rope floats in the corona under a balance between magnetic compression and tension forces. When an eruption occurs, the magnetic compression exceeds the magnetic tension and causes the flux rope to be thrown outwards, away from the Sun. Three important factors which impact the occurrence and evolution of the eruptive processes are investigated. These factors are magnetic reconnection, new emerging flux, and the large scale curvature of the flux rope. First, our new results confirm that in the absence of reconnection, magnetic tension in two-dimensional configuration is always strong enough to prevent escape of the flux rope to infinity after it erupts. However, only a relatively small reconnection rate is needed to allow the flux rope to escape to infinity. Specifically, for a coronal density model that decreases exponentially with height we find that average Alfvén Mach number MA for the inflow into the reconnection site can be as small as M A = 0.005 and still be fast enough to give a plausible eruption. The best fit to observations is obtained by assuming an inflow rate on the order of MA ~ 0.1. Second, we have found that the emergence of new flux system in the vicinity of a preexisting flux rope can cause a loss of ideal-MHD equilibrium under certain circumstances. But the circumstances which lead to eruption are much richer and more complicated than commonly described in the existing literatures. Our model results suggest that the actual circumstances leading to an eruption are sensitive, not only to the polarity of the emerging region, but to several other parameters, such as its strength, distance, and area as well. The results also indicate that in general there is no simple, universal relation between the orientation of the emerging flux and the likelihood of an eruption. Finally, our research shows that the large-scale curvature of a flux rope increases the magnetic compression and helps propel it outwards. We also find that the maximum total magnetic energy which can be stored in our model before equilibrium is lost is 1.53 times the energy of the potential field, which is consistent with the theoretical limit, 1.662, for the fully opened field predicted by Aly [1991] and Sturrock [1991].

A magnetic bearing control approach using flux feedback

NASA Technical Reports Server (NTRS)

Groom, Nelson J.

1989-01-01

A magnetic bearing control approach using flux feedback is described and test results for a laboratory model magnetic bearing actuator are presented. Test results were obtained using a magnetic bearing test fixture, which is also described. The magnetic bearing actuator consists of elements similar to those used in a laboratory test model Annular Momentum Control Device (AMCD).

Magnetic clouds, helicity conservation, and intrinsic scale flux ropes

NASA Technical Reports Server (NTRS)

Kumar, A.; Rust, D. M.

1995-01-01

An intrinsic-scale flux-rope model for interplanetary magnetic clouds, incorporating conservation of magnetic helicity, flux and mass is found to adequately explain clouds' average thermodynamic and magnetic properties. In spite their continuous expansion as they balloon into interplanetary space, magnetic clouds maintain high temperatures. This is shown to be due to magnetic energy dissipation. The temperature of an expanding cloud is shown to pass through a maximum above its starting temperature if the initial plasma beta in the cloud is less than 2/3. Excess magnetic pressure inside the cloud is not an important driver of the expansion as it is almost balanced by the tension in the helical field lines. It is conservation of magnetic helicity and flux that requires that clouds expand radially as they move away from the Sun. Comparison with published data shows good agreement between measured cloud properties and theory. Parameters determined from theoretical fits to the data, when extended back to the Sun, are consistent with the origin of interplanetary magnetic clouds in solar filament eruptions. A possible extension of the heating mechanism discussed here to heating of the solar corona is discussed.

Scanning SQUID sampler with 40-ps time resolution

NASA Astrophysics Data System (ADS)

Cui, Zheng; Kirtley, John R.; Wang, Yihua; Kratz, Philip A.; Rosenberg, Aaron J.; Watson, Christopher A.; Gibson, Gerald W.; Ketchen, Mark B.; Moler, Kathryn. A.

2017-08-01

Scanning Superconducting QUantum Interference Device (SQUID) microscopy provides valuable information about magnetic properties of materials and devices. The magnetic flux response of the SQUID is often linearized with a flux-locked feedback loop, which limits the response time to microseconds or longer. In this work, we present the design, fabrication, and characterization of a novel scanning SQUID sampler with a 40-ps time resolution and linearized response to periodically triggered signals. Other design features include a micron-scale pickup loop for the detection of local magnetic flux, a field coil to apply a local magnetic field to the sample, and a modulation coil to operate the SQUID sampler in a flux-locked loop to linearize the flux response. The entire sampler device is fabricated on a 2 mm × 2 mm chip and can be scanned over macroscopic planar samples. The flux noise at 4.2 K with 100 kHz repetition rate and 1 s of averaging is of order 1 mΦ0. This SQUID sampler will be useful for imaging dynamics in magnetic and superconducting materials and devices.

Scanning SQUID sampler with 40-ps time resolution.

PubMed

Cui, Zheng; Kirtley, John R; Wang, Yihua; Kratz, Philip A; Rosenberg, Aaron J; Watson, Christopher A; Gibson, Gerald W; Ketchen, Mark B; Moler, Kathryn A

2017-08-01

Scanning Superconducting QUantum Interference Device (SQUID) microscopy provides valuable information about magnetic properties of materials and devices. The magnetic flux response of the SQUID is often linearized with a flux-locked feedback loop, which limits the response time to microseconds or longer. In this work, we present the design, fabrication, and characterization of a novel scanning SQUID sampler with a 40-ps time resolution and linearized response to periodically triggered signals. Other design features include a micron-scale pickup loop for the detection of local magnetic flux, a field coil to apply a local magnetic field to the sample, and a modulation coil to operate the SQUID sampler in a flux-locked loop to linearize the flux response. The entire sampler device is fabricated on a 2 mm × 2 mm chip and can be scanned over macroscopic planar samples. The flux noise at 4.2 K with 100 kHz repetition rate and 1 s of averaging is of order 1 mΦ 0 . This SQUID sampler will be useful for imaging dynamics in magnetic and superconducting materials and devices.

Apparatus and method for handling magnetic particles in a fluid

DOEpatents

Holman, David A.; Grate, Jay W.; Bruckner-Lea, Cynthia J.

2000-01-01

The present invention is an apparatus and method for handling magnetic particles suspended in a fluid, relying upon the known features of a magnetic flux conductor that is permeable thereby permitting the magnetic particles and fluid to flow therethrough; and a controllable magnetic field for the handling. The present invention is an improvement wherein the magnetic flux conductor is a monolithic porous foam.

A study of flux control for high-efficiency speed control of variable flux permanent magnet motor

NASA Astrophysics Data System (ADS)

Kim, Young Hyun; Lee, Seong Soo; Lee, Jung Ho

2018-05-01

In this study, we evaluate the performance of permanent magnets (PMs). The efficiency of attraction in the high speed region was studied using the variable flux memory motor (VFMM). It is presented in order to analyze the magnetic characteristics of PMs, using the second quadrant plan data with re- and de-magnetization. In addition, this study focuses on the evaluation of operational characteristics relative to the magnetizing directions according to the d-axis currents, by using one of the finite element solutions. The feasibility of application for the VFMM has been experimentally demonstrated.

Shaped superconductor cylinder retains intense magnetic field

NASA Technical Reports Server (NTRS)

Hildebrandt, A. F.; Wahlquist, H.

1964-01-01

The curve of the inner walls of a superconducting cylinder is plotted from the flux lines of the magnetic field to be contained. This shaping reduces maximum flux densities and permits a stronger and more uniform magnetic field.

Magnetocumulative generator

DOEpatents

Pettibone, Joseph S.; Wheeler, Paul C.

1983-01-01

An improved magnetocumulative generator is described that is useful for producing magnetic fields of very high energy content over large spatial volumes. The polar directed pleated magnetocumulative generator has a housing (100, 101, 102, 103, 104, 105) providing a housing chamber (106) with an electrically conducting surface. The chamber (106) forms a coaxial system having a small radius portion and a large radius portion. When a magnetic field is injected into the chamber (106), from an external source, most of the magnetic flux associated therewith positions itself in the small radius portion. The propagation of an explosive detonation through high-explosive layers (107, 108) disposed adjacent to the housing causes a phased closure of the chamber (106) which sweeps most of the magnetic flux into the large radius portion of the coaxial system. The energy content of the magnetic field is greatly increased by flux stretching as well as by flux compression. The energy enhanced magnetic field is utilized within the housing chamber itself.

Magnetocumulative generator

DOEpatents

Pettibone, J.S.; Wheeler, P.C.

1981-06-08

An improved magnetocumulative generator is described that is useful for producing magnetic fields of very high energy content over large spatial volumes. The polar directed pleated magnetocumulative generator has a housing providing a housing chamber with an electrically conducting surface. The chamber forms a coaxial system having a small radius portion and a large radius portion. When a magnetic field is injected into the chamber, from an external source, most of the magnetic flux associated therewith positions itself in the small radius portion. The propagation of an explosive detonation through high-explosive layers disposed adjacent to the housing causes a phased closure of the chamber which sweeps most of the magnetic flux into the large radius portion of the coaxial system. The energy content of the magnetic field is greatly increased by flux stretching as well as by flux compression. The energy enhanced magnetic field is utilized within the housing chamber itself.

Buildup of a highly twisted magnetic flux rope during a solar eruption.

PubMed

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-06

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Buildup of a highly twisted magnetic flux rope during a solar eruption

NASA Astrophysics Data System (ADS)

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-01

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Pre-flare association of magnetic fields and millimeter-wave radio emission

NASA Technical Reports Server (NTRS)

Mayfield, E. B.; White, K. P., III

1976-01-01

Observations of radio emission at 3.3 mm wavelength associated with magnetic fields in active regions are reported. Results of more than 200 regions during the years 1967-1968 show a strong correlation between peak enhanced millimeter emission, total flux of the longitudinal component of photospheric magnetic fields and the number of flares produced during transit of active regions. For magnetic flux greater than (10 to the 21st power) maxwells flares will occur and for flux of (10 to the 23rd power) maxwells the sum of the H-alpha flare importance numbers is about 40. The peak millimeter enhancement increases with magnetic flux for regions which subsequently flared. Estimates of the magnetic energy available and the correlation with flare production indicate that the photospheric fields and probably chromospheric currents are responsible for the observed pre-flare heating and provide the energy of flares.

Siphon flows in isolated magnetic flux tubes. 3: The equilibrium path of the flux tube arch

NASA Technical Reports Server (NTRS)

Thomas, John H.; Montesinis, Benjamin

1989-01-01

The arched equilibrium path of a thin magnetic flux tube in a plane-stratified, nonmagnetic atmosphere is calculated for cases in which the flux tube contains a steady siphon flow. The large scale mechanical equilibrium of the flux tube involves a balance among the magnetic buoyancy force, the net magnetic tension force due to the curvature of the flux tube axis, and the inertial (centrifugal) force due to the siphon flow along curved streamlines. The ends of the flux tube are assumed to be pinned down by some other external force. Both isothermal and adiabatic siphon flows are considered for flux tubes in an isothermal external atmosphere. For the isothermal case, in the absence of a siphon flow the equilibrium path reduces to the static arch calculated by Parker (1975, 1979). The presence of a siphon flow causes the flux tube arch to bend more sharply, so that magnetic tension can overcome the additional straightening effect of the inertial force, and reduces the maximum width of the arch. The curvature of the arch increases as the siphon flow speed increases. For a critical siphon flow, with supercritical flow in the downstream leg, the arch is asymmetric, with greater curvature in the downstream leg of the arch. Adiabatic flow have qualitatively similar effects, except that adiabatic cooling reduces the buoyancy of the flux tube and thus leads to significantly wider arches. In some cases the cooling is strong enough to create negative buoyancy along sections of the flux tube, requiring upward curvature of the flux tube path along these sections and sometimes leading to unusual equilibrium paths of periodic, sinusoidal form.

Fourier transform magnetic resonance current density imaging (FT-MRCDI) from one component of magnetic flux density.

PubMed

Ider, Yusuf Ziya; Birgul, Ozlem; Oran, Omer Faruk; Arikan, Orhan; Hamamura, Mark J; Muftuler, L Tugan

2010-06-07

Fourier transform (FT)-based algorithms for magnetic resonance current density imaging (MRCDI) from one component of magnetic flux density have been developed for 2D and 3D problems. For 2D problems, where current is confined to the xy-plane and z-component of the magnetic flux density is measured also on the xy-plane inside the object, an iterative FT-MRCDI algorithm is developed by which both the current distribution inside the object and the z-component of the magnetic flux density on the xy-plane outside the object are reconstructed. The method is applied to simulated as well as actual data from phantoms. The effect of measurement error on the spatial resolution of the current density reconstruction is also investigated. For 3D objects an iterative FT-based algorithm is developed whereby the projected current is reconstructed on any slice using as data the Laplacian of the z-component of magnetic flux density measured for that slice. In an injected current MRCDI scenario, the current is not divergence free on the boundary of the object. The method developed in this study also handles this situation.

Intersection collision warning system

DOT National Transportation Integrated Search

1999-04-01

Safety at unsignalized intersections is a major concern. Intersection collisions are one of the most common types of crash, and in the United States, they account for nearly 2 million accidents and 6,700 fatalities every year. However, a fully signal...

Driver eye-scanning behavior at intersections at night.

DOT National Transportation Integrated Search

2009-10-01

This research project analyzed drivers eye scanning behavior at night when approaching signalized : and unsignalized intersections using the data from a head-mounted eye-tracking system during open road : driving on a prescribed route. During the ...

Left-turn lanes at unsignalized median openings.

DOT National Transportation Integrated Search

2014-03-01

Due to the frequent presence of median openings in urban arterial settings, the requirements for the deceleration and : storage of turning vehicles (e.g. AASHTO Green Book) often exceed the available length between two adjacent : openings which leave...

Flux rope evolution in interplanetary coronal mass ejections: the 13 May 2005 event

NASA Astrophysics Data System (ADS)

Manchester, W. B., IV; van der Holst, B.; Lavraud, B.

2014-06-01

Coronal mass ejections (CMEs) are a dramatic manifestation of solar activity that release vast amounts of plasma into the heliosphere, and have many effects on the interplanetary medium and on planetary atmospheres, and are the major driver of space weather. CMEs occur with the formation and expulsion of large-scale magnetic flux ropes from the solar corona, which are routinely observed in interplanetary space. Simulating and predicting the structure and dynamics of these interplanetary CME magnetic fields are essential to the progress of heliospheric science and space weather prediction. We discuss the simulation of the 13 May 2005 CME event in which we follow the propagation of a flux rope from the solar corona to beyond Earth orbit. In simulating this event, we find that the magnetic flux rope reconnects with the interplanetary magnetic field, to evolve to an open configuration and later reconnects to reform a twisted structure sunward of the original rope. Observations of the 13 May 2005 CME magnetic field near Earth suggest that such a rearrangement of magnetic flux by reconnection may have occurred.

The effects of mobile phone use on pedestrian crossing behaviour at signalized and unsignalized intersections.

PubMed

Hatfield, Julie; Murphy, Susanne

2007-01-01

Research amongst drivers suggests that pedestrians using mobile telephones may behave riskily while crossing the road, and casual observation suggests concerning levels of pedestrian mobile-use. An observational field survey of 270 females and 276 males was conducted to compare the safety of crossing behaviours for pedestrians using, versus not using, a mobile phone. Amongst females, pedestrians who crossed while talking on a mobile phone crossed more slowly, and were less likely to look at traffic before starting to cross, to wait for traffic to stop, or to look at traffic while crossing, compared to matched controls. For males, pedestrians who crossed while talking on a mobile phone crossed more slowly at unsignalized crossings. These effects suggest that talking on a mobile phone is associated with cognitive distraction that may undermine pedestrian safety. Messages explicitly suggesting techniques for avoiding mobile-use while road crossing may benefit pedestrian safety.

Toroidal-Core Microinductors Biased by Permanent Magnets

NASA Technical Reports Server (NTRS)

Lieneweg, Udo; Blaes, Brent

2003-01-01

The designs of microscopic toroidal-core inductors in integrated circuits of DC-to-DC voltage converters would be modified, according to a proposal, by filling the gaps in the cores with permanent magnets that would apply bias fluxes (see figure). The magnitudes and polarities of the bias fluxes would be tailored to counteract the DC fluxes generated by the DC components of the currents in the inductor windings, such that it would be possible to either reduce the sizes of the cores or increase the AC components of the currents in the cores without incurring adverse effects. Reducing the sizes of the cores could save significant amounts of space on integrated circuits because relative to other integrated-circuit components, microinductors occupy large areas - of the order of a square millimeter each. An important consideration in the design of such an inductor is preventing magnetic saturation of the core at current levels up to the maximum anticipated operating current. The requirement to prevent saturation, as well as other requirements and constraints upon the design of the core are expressed by several equations based on the traditional magnetic-circuit approximation. The equations involve the core and gap dimensions and the magnetic-property parameters of the core and magnet materials. The equations show that, other things remaining equal, as the maximum current is increased, one must increase the size of the core to prevent the flux density from rising to the saturation level. By using a permanent bias flux to oppose the flux generated by the DC component of the current, one would reduce the net DC component of flux in the core, making it possible to reduce the core size needed to prevent the total flux density (sum of DC and AC components) from rising to the saturation level. Alternatively, one could take advantage of the reduction of the net DC component of flux by increasing the allowable AC component of flux and the corresponding AC component of current. In either case, permanent-magnet material and the slant (if any) and thickness of the gap must be chosen according to the equations to obtain the required bias flux. In modifying the design of the inductor, one must ensure that the inductance is not altered. The simplest way to preserve the original value of inductance would be to leave the gap dimensions unchanged and fill the gap with a permanent- magnet material that, fortuitously, would produce just the required bias flux. A more generally applicable alternative would be to partly fill either the original gap or a slightly enlarged gap with a suitable permanent-magnet material (thereby leaving a small residual gap) so that the reluctance of the resulting magnetic circuit would yield the desired inductance.

Magnetic flux transport of decaying active regions and enhanced magnetic network. [of solar supergranulation

NASA Technical Reports Server (NTRS)

Wang, Haimin; Zirin, Harold; Ai, Guoxiang

1991-01-01

Several series of coordinated observations on decaying active regions and enhanced magnetic network regions on the sun were carried out jointly at Big Bear Solar Observatory and at the Huairou Solar Observing Station of the Bejing Astronomical Observatory in China. The magnetic field evolution in several regions was followed closely for three to seven days. The magnetic flux transport from the remnants of decayed active regions was studied, along with the evolution and lifetime of the magnetic network which defines the boundaries of supergranules. The magnetic flux transport in an enhanced network region was studied in detail and found to be negative. Also briefly described are some properties of moving magnetic features around a sunspot. Results of all of the above studies are presented.

Analysis and Optimization of a Novel 2-D Magnet Array with Gaps and Staggers for a Moving-Magnet Planar Motor

PubMed Central

Chen, Xuedong; Zeng, Lizhan

2018-01-01

This paper presents a novel 2-D magnet array with gaps and staggers, which is especially suitable for magnetically levitated planar motor with moving magnets. The magnetic flux density distribution is derived by Fourier analysis and superposition. The influences of gaps and staggers on high-order harmonics and flux density were analyzed, and the optimized design is presented. Compared with the other improved structures based on traditional Halbach magnet arrays, the proposed design has the lowest high-order harmonics percentage, and the characteristics of flux density meet the demand of high acceleration in horizontal directions. It is also lightweight and easy to manufacture. The proposed magnet array was built, and the calculation results have been verified with experiment. PMID:29300323

Genesis of Interplanetary Intermittent Turbulence: a Case Study of Rope-Rope Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Chian, Abraham C.- L.; Feng, Heng Q.; Hu, Qiang; Loew, Murray H.; Miranda, Rodrigo A.; Munoz, Pablo R.; Sibeck, David G.; Wu, De J.

2016-01-01

In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope-rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event. The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.

Unique topological characterization of braided magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeates, A. R.; Hornig, G.

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line, or the average pairwise crossing number between a given field line and all others. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove thatmore » it uniquely characterizes the field line mapping and hence the magnetic topology.« less

Nonlinear restrictions on dynamo action. [in magnetic fields of astrophysical objects

NASA Technical Reports Server (NTRS)

Vainshtein, Samuel I.; Cattaneo, Fausto

1992-01-01

Astrophysical dynamos operate in the limit of small magnetic diffusivity. In order for magnetic reconnection to occur, very small magnetic structures must form so that diffusion becomes effective. The formation of small-scale fields is accompanied by the stretching of the field lines and therefore by an amplification of the magnetic field strength. The back reaction of the magnetic field on the motions leads to the eventual saturation of the dynamo process, thus posing a constraint on the amount of magnetic flux that can be generated by dynamo action, It is argued that in the limit of small diffusivity only a small amount of flux, many orders of magnitude less than the observed fluxes, can be created by dynamo processes.

Magnetic refrigeration using flux compression in superconductors

NASA Technical Reports Server (NTRS)

Israelsson, U. E.; Strayer, D. M.; Jackson, H. W.; Petrac, D.

1990-01-01

The feasibility of using flux compression in high-temperature superconductors to produce the large time-varying magnetic fields required in a field cycled magnetic refrigerator operating between 20 K and 4 K is presently investigated. This paper describes the refrigerator concept and lists limitations and advantages in comparison with conventional refrigeration techniques. The maximum fields obtainable by flux compression in high-temperature supercoductor materials, as presently prepared, are too low to serve in such a refrigerator. However, reports exist of critical current values that are near usable levels for flux pumps in refrigerator applications.

Electron heat flux dropouts in the solar wind - Evidence for interplanetary magnetic field reconnection?

NASA Technical Reports Server (NTRS)

Mccomas, D. J.; Gosling, J. T.; Phillips, J. L.; Bame, S. J.; Luhmann, J. G.; Smith, E. J.

1989-01-01

An examination of ISEE-3 data from 1978 reveal 25 electron heat flux dropout events ranging in duration from 20 min to over 11 hours. The heat flux dropouts are found to occur in association with high plasma densities, low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. It is suggested that the heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the sun and instead are connected to the outer heliosphere at both ends.

Photospheric Magnetic Flux Transport - Supergranules Rule

NASA Technical Reports Server (NTRS)

Hathaway, David H.; Rightmire-Upton, Lisa

2012-01-01

Observations of the transport of magnetic flux in the Sun's photosphere show that active region magnetic flux is carried far from its origin by a combination of flows. These flows have previously been identified and modeled as separate axisymmetric processes: differential rotation, meridional flow, and supergranule diffusion. Experiments with a surface convective flow model reveal that the true nature of this transport is advection by the non-axisymmetric cellular flows themselves - supergranules. Magnetic elements are transported to the boundaries of the cells and then follow the evolving boundaries. The convective flows in supergranules have peak velocities near 500 m/s. These flows completely overpower the superimposed 20 m/s meridional flow and 100 m/s differential rotation. The magnetic elements remain pinned at the supergranule boundaries. Experiments with and without the superimposed axisymmetric photospheric flows show that the axisymmetric transport of magnetic flux is controlled by the advection of the cellular pattern by underlying flows representative of deeper layers. The magnetic elements follow the differential rotation and meridional flow associated with the convection cells themselves -- supergranules rule!

Flux lattice imaging of a patterned niobium thin film

NASA Astrophysics Data System (ADS)

Roseman, M.; Grütter, P.; Badía, A.; Metlushko, V.

2001-06-01

Using our cryogenic magnetic force microscope, we have investigated a superconducting Nb thin film, 100 nm in thickness with Tc˜6.5 K. The film is patterned with a square array (1 μm×1 μm) of antidots, which serve as artificial pinning centers for magnetic flux. We have observed flux lattice matching as a function of applied magnetic field and temperature, for field strengths up to the third matching field, with evidence of flux dragging by the tip around the antidots. Force gradient distance curves acquired at temperatures about Tc clearly demonstrate an observable Meissner force between tip and sample, and allow for an estimation of the magnetic screening penetration depth.

Sigmoidal equilibria and eruptive instabilities in laboratory magnetic flux ropes

NASA Astrophysics Data System (ADS)

Myers, C. E.; Yamada, M.; Belova, E.; Ji, H.; Yoo, J.

2013-12-01

The Magnetic Reconnection Experiment (MRX) has recently been modified to study quasi-statically driven line-tied magnetic flux ropes in the context of storage-and-release eruptions in the corona. Detailed in situ magnetic measurements and supporting MHD simulations permit quantitative analysis of the plasma behavior. We find that the behavior of these flux ropes depends strongly on the properties of the applied potential magnetic field arcade. For example, when the arcade is aligned parallel to the flux rope footpoints, force free currents induced in the expanding rope modify the pressure and tension in the arcade, resulting in a confined, quiescent discharge with a saturated kink instability. When the arcade is obliquely aligned to the footpoints, on the other hand, a highly sigmoidal equilibrium forms that can dynamically erupt (see Fig. 1 and Fig. 2). To our knowledge, these storage-and-release eruptions are the first of their kind to be produced in the laboratory. A new 2D magnetic probe array is used to map out the internal structure of the flux ropes during both the storage and the release phases of the discharge. The kink instability and the torus instability are studied as candidate eruptive mechanisms--the latter by varying the vertical gradient of the potential field arcade. We also investigate magnetic reconnection events that accompany the eruptions. The long-term objective of this work is to use internal magnetic measurements of the flux rope structure to better understand the evolution and eruption of comparable structures in the corona. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the Center for Magnetic Self-Organization (CMSO). Qualitative sketches of flux ropes formed in (1) a parallel potential field arcade; and (2) an oblique potential field arcade. One-dimensional magnetic measurements from (1) a parallel arcade discharge that is confined; and (2) an oblique arcade discharge that erupts.

Runaway electrons and magnetic island confinement

DOE PAGES

Boozer, Allen H.

2016-08-19

The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativisticmore » energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. Furthermore, the physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.« less

Simulation of the small-scale magnetism in main-sequence stellar atmospheres

NASA Astrophysics Data System (ADS)

Salhab, R. G.; Steiner, O.; Berdyugina, S. V.; Freytag, B.; Rajaguru, S. P.; Steffen, M.

2018-06-01

Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral lines. Aims: In this paper, properties of the small-scale magnetism of four cool stellar atmospheres, including the Sun, are investigated, and in particular its effects on the radiative intensity and flux. Methods: We carried out three-dimensional radiation magnetohydrodynamic simulations with the CO5BOLD code in two different settings: with and without a magnetic field. These are thought to represent states of high and low small-scale magnetic activity of a stellar magnetic cycle. Results: We find that the presence of small-scale magnetism increases the bolometric intensity and flux in all investigated models. The surplus in radiative flux of the magnetic over the magnetic field-free atmosphere increases with increasing effective temperature, Teff, from 0.47% for spectral type K8V to 1.05% for the solar model, but decreases for higher effective temperatures than solar. The degree of evacuation of the magnetic flux concentrations monotonically increases with Teff as does their depression of the visible optical surface, that is the Wilson depression. Nevertheless, the strength of the field concentrations on this surface stays remarkably unchanged at ≈1560 G throughout the considered range of spectral types. With respect to the surrounding gas pressure, the field strength is close to (thermal) equipartition for the Sun and spectral type F5V but is clearly sub-equipartition for K2V and more so for K8V. The magnetic flux concentrations appear most conspicuous for model K2V owing to their high brightness contrast. Conclusions: For mean magnetic flux densities of approximately 50 G, we expect the small-scale magnetism of stars in the spectral range from F5V to K8V to produce a positive contribution to their bolometric luminosity. The modulation seems to be most effective for early G-type stars.

Runaway electrons and magnetic island confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boozer, Allen H., E-mail: ahb17@columbia.edu

The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativisticmore » energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. The physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.« less

Runaway electrons and magnetic island confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boozer, Allen H.

The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativisticmore » energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. Furthermore, the physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.« less

Effect of gravitational stratification on the propagation of a CME

NASA Astrophysics Data System (ADS)

Pagano, P.; Mackay, D. H.; Poedts, S.

2013-12-01

Context. Coronal mass ejections (CMEs) are the most violent phenomenon found on the Sun. One model that explains their occurrence is the flux rope ejection model. A magnetic flux rope is ejected from the solar corona and reaches the interplanetary space where it interacts with the pre-existing magnetic fields and plasma. Both gravity and the stratification of the corona affect the early evolution of the flux rope. Aims: Our aim is to study the role of gravitational stratification on the propagation of CMEs. In particular, we assess how it influences the speed and shape of CMEs and under what conditions the flux rope ejection becomes a CME or when it is quenched. Methods: We ran a set of MHD simulations that adopt an eruptive initial magnetic configuration that has already been shown to be suitable for a flux rope ejection. We varied the temperature of the backgroud corona and the intensity of the initial magnetic field to tune the gravitational stratification and the amount of ejected magnetic flux. We used an automatic technique to track the expansion and the propagation of the magnetic flux rope in the MHD simulations. From the analysis of the parameter space, we evaluate the role of gravitational stratification on the CME speed and expansion. Results: Our study shows that gravitational stratification plays a significant role in determining whether the flux rope ejection will turn into a full CME or whether the magnetic flux rope will stop in the corona. The CME speed is affected by the background corona where it travels faster when the corona is colder and when the initial magnetic field is more intense. The fastest CME we reproduce in our parameter space travels at ~850 km s-1. Moreover, the background gravitational stratification plays a role in the side expansion of the CME, and we find that when the background temperature is higher, the resulting shape of the CME is flattened more. Conclusions: Our study shows that although the initiation mechanisms of the CME are purely magnetic, the background coronal plasma plays a key role in the CME propagation, and full MHD models should be applied when one focuses especially on the production of a CME from a flux rope ejection. Movies are available in electronic form at http://www.aanda.org

A study of flux transfer events at different planets

NASA Technical Reports Server (NTRS)

Russell, C. T.

1995-01-01

Flux transfer events (FTEs) are disturbances in and near the magnetopause current layer that cause a characteristic signature in the component of the magnetic field parallel to the average boundary normal. These disturbances have been observed at Mercury, Earth and Jupiter but not at Saturn, Uranus or Neptune. At Earth, FTEs last about 1 minute and repeat about every 8 but at Mercury, a much smaller magnetosphere, the events last seconds and are tens of seconds apart. These features have been interpreted in terms of magnetospheric flux ropes connected to the interplanetary magnetic field, arising as the result of reconnection. An analogous phenomenon occurs at Venus where magnetic flux ropes arise at the ionosphere, a boundary between a very strongly magnetized one. However, here the flux ropes do not appear to be due to reconnection.

The global distribution of magnetic helicity in the solar corona

NASA Astrophysics Data System (ADS)

Yeates, A. R.; Hornig, G.

2016-10-01

By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden bursts of helicity output, in contrast to the steady flux along the open magnetic field lines. Movies are available at http://www.aanda.org

Dual-keel electrodynamic maglev system

DOEpatents

He, Jianliang; Wang, Zian; Rote, Donald M.; Coffey, Howard T.; Hull, John R.; Mulcahy, Thomas M.; Cal, Yigang

1996-01-01

A propulsion and stabilization system with a plurality of superconducting magnetic devices affixed to the dual-keels of a vehicle, where the superconducting magnetic devices produce a magnetic field when energized. The system also includes a plurality of figure-eight shaped null-flux coils affixed to opposing vertical sides of slots in a guideway. The figure-eight shaped null-flux coils are vertically oriented, laterally cross-connected in parallel, longitudinally connected in series, and continue the length of the vertical slots providing levitation and guidance force. An external power source energizes the figure-eight shaped null-flux coils to create a magnetic traveling wave that interacts with the magnetic field produced by the superconducting magnets to impart motion to the vehicle.

Knotty structures of the evolving heliospheric magnetic fields.

NASA Astrophysics Data System (ADS)

Roth, Ilan

2013-04-01

The analogy between MHD and knot theory is utilized in an analysis of structure, stability and evolution of complex magnetic heliospheric flux tubes. Planar projection of a three-dimensional magnetic configuration depicts the structure as a two-dimensional diagram with crossings, to which one may assign mathematical operations leading to robust topological invariants. These invariants enrich the topological information of magnetic configurations beyond helicity. It is conjectured that the field which emerges from the solar photosphere is structured as one of simplest knot invariants - unknot or prime knot, and these flux ropes are then stretched while carried by the solar wind into the interplanetary medium. Preservation of invariants for small diffusivity and large cross section of the emerging magnetic flux makes them impervious to large scale reconnection, allowing us to predict the observed structures at 1AU as elongated prime knots. Similar structures may be observed in magnetic clouds which got disconnected from their foot-points and in ion drop-out configurations from a compact flare source in solar impulsive solar events. Observation of small scale magnetic features consistent with prime knot may indicate spatial intermittency and non-Gaussian statistics in the turbulent cascade process. For flux tubes with higher resistivity, magnetic energy decay rate should decrease with increased knot complexity as the invariants are then harder to be violated. Future measurements are suggested for distinctly oriented magnetic fields with directionally varying suprathermal particle fluxes.

A finite element calculation of flux pumping

NASA Astrophysics Data System (ADS)

Campbell, A. M.

2017-12-01

A flux pump is not only a fascinating example of the power of Faraday’s concept of flux lines, but also an attractive way of powering superconducting magnets without large electronic power supplies. However it is not possible to do this in HTS by driving a part of the superconductor normal, it must be done by exceeding the local critical density. The picture of a magnet pulling flux lines through the material is attractive, but as there is no direct contact between flux lines in the magnet and vortices, unless the gap between them is comparable to the coherence length, the process must be explicable in terms of classical electromagnetism and a nonlinear V-I characteristic. In this paper a simple 2D model of a flux pump is used to determine the pumping behaviour from first principles and the geometry. It is analysed with finite element software using the A formulation and FlexPDE. A thin magnet is passed across one or more superconductors connected to a load, which is a large rectangular loop. This means that the self and mutual inductances can be calculated explicitly. A wide strip, a narrow strip and two conductors are considered. Also an analytic circuit model is analysed. In all cases the critical state model is used, so the flux flow resistivity and dynamic resistivity are not directly involved, although an effective resistivity appears when J c is exceeded. In most of the cases considered here is a large gap between the theory and the experiments. In particular the maximum flux transferred to the load area is always less than the flux of the magnet. Also once the threshold needed for pumping is exceeded the flux in the load saturates within a few cycles. However the analytic circuit model allows a simple modification to allow for the large reduction in I c when the magnet is over a conductor. This not only changes the direction of the pumped flux but leads to much more effective pumping.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael, A. T.; Opher, M.; Provornikova, E.

In the heliosheath (HS), Voyager 2 has observed a flow with constant radial velocity and magnetic flux conservation. Voyager 1, however, has observed a decrease in the flow’s radial velocity and an order of magnitude decrease in magnetic flux. We investigate the role of the 11 yr solar cycle variation of the magnetic field strength on the magnetic flux within the HS using a global 3D magnetohydrodynamic model of the heliosphere. We use time and latitude-dependent solar wind velocity and density inferred from Solar and Heliospheric Observatory/SWAN and interplanetary scintillations data and implemented solar cycle variations of the magnetic fieldmore » derived from 27 day averages of the field magnitude average of the magnetic field at 1 AU from the OMNI database. With the inclusion of the solar cycle time-dependent magnetic field intensity, the model matches the observed intensity of the magnetic field in the HS along both Voyager 1 and 2. This is a significant improvement from the same model without magnetic field solar cycle variations, which was over a factor of two larger. The model accurately predicts the radial velocity observed by Voyager 2; however, the model predicts a flow speed ∼100 km s{sup −1} larger than that derived from LECP measurements at Voyager 1. In the model, magnetic flux is conserved along both Voyager trajectories, contrary to observations. This implies that the solar cycle variations in solar wind magnetic field observed at 1 AU does not cause the order of magnitude decrease in magnetic flux observed in the Voyager 1 data.« less

Storage-and-release flux rope eruptions in the laboratory: initial results and experimental plans

NASA Astrophysics Data System (ADS)

Myers, C. E.; Yamada, M.; Ji, H.; Yoo, J.; Jara-Almonte, J.; Lawrence, E. E.

2012-12-01

Solar eruptive events such as coronal mass ejections (CMEs) are thought to be driven by a sudden release of magnetic energy stored in the corona. In many cases, the pre-eruptive configuration is a non-potential magnetic structure that can be modeled as a line-tied magnetic flux rope. In spite of ever-improving observational capabilities, directly studying the evolution of coronal flux ropes remains a significant challenge. Thus, in order to further explore the mechanisms that drive solar eruptions, we must find novel ways to simulate the relevant physical system. To this end, we have constructed a new laboratory experiment to study storage-and-release flux rope eruptions. This experiment contains a carefully designed set of ``sub-photospheric" coils that produces an active-region-like potential field configuration that remains static throughout the discharge. An arched magnetic flux rope plasma is formed within this potential field configuration by driving electric current through two line-tied footpoints (copper electrodes). Over the course of the discharge, the plasma current is quasi-statically increased (to tens of kiloamperes over many Alfvén times) in order to slowly build up magnetic energy in the system. As the flux rope gains energy, it will expand away from the electrodes to a point where it is expected to undergo a dynamic eruption due to the onset of a loss-of-equilibrium [Forbes & Isenberg, Astrophys. J. 373, 294 (1991)] or the torus instability [Kliem & Török, Phys. Rev. Lett. 96, 255002 (2006)]. In these experiments, the structure of the background potential field configuration (i.e., the field decay index) can be varied to study its effect on the observed flux rope eruptions. Initial results from these experiment are presented, including images from a fast visible light camera and direct measurements from internal magnetic diagnostics. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the Center for Magnetic Self-Organization (CMSO).; Specially designed magnetic field coils (orange and blue) are used to produce an active-region-like potential field configuration within the vacuum vessel (gray). An arched magnetic flux rope plasma is formed by driving electric current along low-lying potential field lines (blue/green). As magnetic energy builds up in the flux rope, it will expand outward and possibly undergo a storage-and-release eruption.

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

NASA Astrophysics Data System (ADS)

Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.

2004-12-01

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (Bθ ≤ 100 Gauss, L=90 cm, r≤3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / Bθ > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t≤ 20 τ Alfv´ {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

NASA Astrophysics Data System (ADS)

Furno, Ivo

2004-11-01

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20τ_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Reconnection Fluxes in Eruptive and Confined Flares and Implications for Superflares on the Sun

NASA Astrophysics Data System (ADS)

Tschernitz, Johannes; Veronig, Astrid M.; Thalmann, Julia K.; Hinterreiter, Jürgen; Pötzi, Werner

2018-01-01

We study the energy release process of a set of 51 flares (32 confined, 19 eruptive) ranging from GOES class B3 to X17. We use Hα filtergrams from Kanzelhöhe Observatory together with Solar Dynamics Observatory HMI and Solar and Heliospheric Observatory MDI magnetograms to derive magnetic reconnection fluxes and rates. The flare reconnection flux is strongly correlated with the peak of the GOES 1–8 Å soft X-ray flux (c = 0.92, in log–log space) for both confined and eruptive flares. Confined flares of a certain GOES class exhibit smaller ribbon areas but larger magnetic flux densities in the flare ribbons (by a factor of 2). In the largest events, up to ≈50% of the magnetic flux of the active region (AR) causing the flare is involved in the flare magnetic reconnection. These findings allow us to extrapolate toward the largest solar flares possible. A complex solar AR hosting a magnetic flux of 2 × 1023 Mx, which is in line with the largest AR fluxes directly measured, is capable of producing an X80 flare, which corresponds to a bolometric energy of about 7 × 1032 erg. Using a magnetic flux estimate of 6 × 1023 Mx for the largest solar AR observed, we find that flares of GOES class ≈X500 could be produced (E bol ≈ 3 × 1033 erg). These estimates suggest that the present day’s Sun is capable of producing flares and related space weather events that may be more than an order of magnitude stronger than have been observed to date.

Substorms At Jupiter: Galileo Observations of Transient Reconnection in The Near Tail

NASA Technical Reports Server (NTRS)

Russell, C. T.; Khurana, K. K.; Kivelson, M. G.; Huddleston, D. E.

2000-01-01

The magnetic flux content of the Jovian magnetosphere is set by the internal dynamo, but those magnetic field lines are constantly being loaded by heavy ions at the orbit of lo and dragged inexorably outward by the centrifugal force. Vasyliunas has proposed a steady state reconnecting magnetospheric model that sheds plasma islands of zero net magnetic flux and returns nearly empty flux tubes to the inner magnetosphere. The Galileo observations indicate that beyond 40 Rj the current sheet begins to tear and beyond 50 Rj on the nightside explosively reconnects as the tearing site reaches the low density lobe region above and below the current sheet. Small events occur irregularly but on average about every 4 hours and large events about once a day. The magnetic flux reconnected in such events amounts up to about 70,000 Webers/sec and is sufficient to return the outwardly convected magnetic flux to the inner magnetosphere. Since this process releases plasmoids into the jovian tail, as do terrestrial substorms; since this process involves explosive reconnection across the current sheet on the nightside of the planet, as do terrestrial substorms; and since the process is a key in closing the circulation pattern of the magnetic and plasma flux, as it is in terrestrial substorms; we refer to these events as jovian substorms.

SELF-CANCELLATION OF EPHEMERAL REGIONS IN THE QUIET SUN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shuhong; Zhang, Jun; Li, Ting

2012-06-20

With the observations from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, we statistically investigate the ephemeral regions (ERs) in the quiet Sun. We find that there are two types of ERs: normal ERs (NERs) and self-canceled ERs (SERs). Each NER emerges and grows with separation of its opposite polarity patches which will cancel or coalesce with other surrounding magnetic flux. Each SER also emerges and grows and its dipolar patches separate at first, but a part of the magnetic flux of the SER will move together and cancel gradually, which is described with the term 'self-cancellation' bymore » us. We identify 2988 ERs, among which there are 190 SERs, about 6.4% of the ERs. The mean value of self-cancellation fraction of SERs is 62.5%, and the total self-canceled flux of SERs is 9.8% of the total ER flux. Our results also reveal that the higher the ER magnetic flux is, (1) the easier the performance of ER self-cancellation is, (2) the smaller the self-cancellation fraction is, and (3) the more the self-canceled flux is. We think that the self-cancellation of SERs is caused by the submergence of magnetic loops connecting the dipolar patches, without magnetic energy release.« less

Higher-order aberrations and best-corrected visual acuity in Native American children with a high prevalence of astigmatism

PubMed Central

Miller, Joseph M.; Harvey, Erin M.; Schwiegerling, Jim

2016-01-01

Purpose To determine whether higher-order aberrations (HOAs) in children from a highly astigmatic population differ from population norms and whether HOAs are associated with astigmatism and reduced best-corrected visual acuity. Methods Subjects were 218 Tohono O’odham Native American children 5–9 years of age. Noncycloplegic HOA measurements were obtained with a handheld Shack-Hartmann sensor (SHS). Signed (z06s to z14s) and unsigned (z06u to z14u) wavefront aberration Zernike coefficients Z(3,−3) to Z(4,4) were rescaled for a 4 mm diameter pupil and compared to adult population norms. Cycloplegic refraction and best-corrected logMAR letter visual acuity (BCVA) were also measured. Regression analyses assessed the contribution of astigmatism (J0) and HOAs to BCVA. Results The mean root-mean-square (RMS) HOA of 0.191 ± 0.072 μm was significantly greater than population norms (0.100 ± 0.044 μm. All unsigned HOA coefficients (z06u to z14u) and all signed coefficients except z09s, z10s, and z11s were significantly larger than population norms. Decreased BCVA was associated with astigmatism (J0) and spherical aberration (z12u) but not RMS coma, with the effect of J0 about 4 times as great as z12u. Conclusions Tohono O’odham children show elevated HOAs compared to population norms. Astigmatism and unsigned spherical aberration are associated with decreased acuity, but the effects of spherical aberration are minimal and not clinically significant. PMID:26239206

The role of 'jackpot' stimuli in maladaptive decision-making: dissociable effects of D1/D2 receptor agonists and antagonists.

PubMed

Smith, Aaron P; Hofford, Rebecca S; Zentall, Thomas R; Beckmann, Joshua S

2018-05-01

Laboratory experiments often model risk through a choice between a large, uncertain (LU) reward against a small, certain (SC) reward as an index of an individual's risk tolerance. An important factor generally lacking from these procedures are reward-associated cues that may modulate risk preferences. We tested whether the addition of cues signaling 'jackpot' wins to LU choices would modulate risk preferences and if these cue effects were mediated by dopaminergic signaling. Three groups of rats chose between LU and SC rewards for which the LU probability of reward decreased across blocks. The unsignaled group received a non-informative stimulus of trial outcome. The signaled group received a jackpot signal prior to reward delivery and blackout on losses. The signaled-light group received a similar jackpot for wins, but a salient loss signal distinct from the win signal. Presenting win signals decreased the discounting of LU value for both signaled groups regardless of loss signal, while the unsignaled group showed discounting similar to previous research without cues. Pharmacological challenges with D1/D2 agonists and antagonists revealed that D1 antagonism increased and decreased sensitives to the relative probability of reward for unsignaled and signaled groups, respectively, while D2 agonists decreased sensitivities to the relative magnitude of reward. The results highlight how signals predictive of wins can promote maladaptive risk taking in individuals, while loss signals have reduced effect. Additionally, the presence of reward-predictive cues may change the underlying neurobehavioral mechanisms mediating decision-making under risk.

Magnetospheric Multiscale Mission Observations of Magnetic Flux Ropes in the Earth's Plasma Sheet

NASA Astrophysics Data System (ADS)

Slavin, J. A.; Akhavan-Tafti, M.; Poh, G.; Le, G.; Russell, C. T.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Gershman, D. J.; Pollock, C. J.; Giles, B. L.; Moore, T. E.; Burch, J. L.

2017-12-01

A major discovery by the Cluster mission and the previous generation of science missions is the presence of earthward and tailward moving magnetic flux ropes in the Earth's plasma sheet. However, the lack of high-time resolution plasma measurements severely limited progress concerning the formation and evolution of these reconnection generated structures. We use high-time resolution magnetic and electric field and plasma measurements from the Magnetospheric Multiscale mission's first tail season to investigate: 1) the distribution of flux rope diameters relative to the local ion and electron inertial lengths; 2) the internal force balance sustaining these structures; and 3) the magnetic connectivity of the flux ropes to the Earth and/or the interplanetary medium; 4) the specific entropy of earthward moving flux ropes and the possible effect of "buoyancy" on how deep they penetrate into the inner magnetosphere; and 5) evidence for coalescence of adjacent flux ropes and/or the division of existing flux ropes through the formation of secondary X-lines. The results of these initial analyses will be discussed in terms of their implications for reconnection-driven magnetospheric dynamics and substorms.

Design and analysis of a new flux-intensifying permanent magnet brushless motor with multilayer flux barriers

NASA Astrophysics Data System (ADS)

Yang, Shen; Zhu, Xiaoyong; Xiang, Zixuan; Fan, Deyang; Wu, Wenye; Yin, Jianing

2017-05-01

This paper proposes a new flux-intensifying permanent magnet brushless motor for potential application in electric vehicles. The key of the proposed motor is to adopt the concept of flux-intensifying effect, thus the preferable flux-weakening ability and extended speed range can be achieved. The usage of segmented and relatively thinner permanent magnet (PM) in the proposed motor contributes to the increase of d-axis inductance Ld. In addition, the multilayer flux barriers along q-axis flux path will effectively decrease q-axis inductance Lq. As a result, the unique feature of Ld>Lq can be obtained, which is beneficial to extending the speed range of the proposed motor. Furthermore, the flux-intensifying effect can reduce the risk of irreversible demagnetization in PMs. The electromagnetic performances of the proposed motor are analyzed and investigated in details by using the finite element methods, which demonstrate the excellent flux-weakening capability and wide speed range can be achieved in the proposed FI-PMBL motor.

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

DOE PAGES

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

2016-08-26

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, T. A.; DeForest, C. E., E-mail: howard@boulder.swri.edu

We present a data-driven narrative of the launch and early evolution of the magnetic structure that gave rise to the coronal mass ejection (CME) on 2008 December 12. The structure formed on December 7 and launched early on December 12. We interpret this structure as a flux rope based on prelaunch morphology, postlaunch magnetic measurements, and the lack of large-scale magnetic reconnection signatures at launch. We ascribe three separate onset mechanisms to the complete disconnection of the flux rope from the Sun. It took 19 hr for the flux rope to be fully removed from the Sun, by which timemore » the segment that first disconnected was around 40 R {sub ☉} away. This implies that the original flux rope was stretched or broken; we provide evidence for a possible bisection. A transient dark arcade was observed on the Sun that was later obscured by a bright arcade, which we interpret as the strapping field stretching and magnetically reconnecting as it disconnected from the coronal field. We identify three separate structures in coronagraph images to be manifestations of the same original flux rope, and we describe the implications for CME interpretation. We cite the rotation in the central flux rope vector of the magnetic clouds observed in situ by ACE/Wind and STEREO-B as evidence of the kink instability of the eastern segment of the flux rope. Finally, we discuss possible alternative narratives, including multiple prelaunch magnetic structures and the nonflux rope scenario. Our results support the view that, in at least some CMEs, flux rope formation occurs before launch.« less

Reconnecting flux-rope dynamo.

PubMed

Baggaley, Andrew W; Barenghi, Carlo F; Shukurov, Anvar; Subramanian, Kandaswamy

2009-11-01

We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit R_{m}-->infinity for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares.

Experimental investigation of multi-scale non-equilibrium plasma dynamics

NASA Astrophysics Data System (ADS)

Bellan, Paul

2013-10-01

Lab experiments at Caltech resolve complex, detailed MHD dynamics spatially and temporally. Unbalanced forces drive fast plasma flows which tend to self-collimate via self-pinching. Collimation results from flow stagnation compressing embedded magnetic flux and so amplifying the magnetic field responsible for pinching. Measurements show that the collimated flow is essentially a dense plasma jet with embedded axial and azimuthal magnetic fields, i.e., a magnetic flux tube (flux rope). The measured jet velocity is in good agreement with an MHD acceleration model. Depending on how flux tube radius varies with axial position, jets flow into a flux tube from both ends or from just one end. Jets kink when the flux tube in which they are embedded breaches the Kruskal-Shafranov stability limit. The lateral acceleration of a sufficiently strong kink can produce an enormous effective gravity which provides the environment for an observed fine-scale, extremely fast Rayleigh-Taylor (RT) instability. The RT can erode the jet current channel to be smaller than the ion skin depth so there is a cascade from the ideal MHD scale of the kink to the non-MHD ion skin depth scale. This process can result in a magnetic reconnection whereby the jet and its embedded flux tube break. Supported by USDOE.

Dynamic topology and flux rope evolution during non-linear tearing of 3D null point current sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wyper, P. F., E-mail: peterw@maths.dundee.ac.uk; Pontin, D. I., E-mail: dpontin@maths.dundee.ac.uk

2014-10-15

In this work, the dynamic magnetic field within a tearing-unstable three-dimensional current sheet about a magnetic null point is described in detail. We focus on the evolution of the magnetic null points and flux ropes that are formed during the tearing process. Generally, we find that both magnetic structures are created prolifically within the layer and are non-trivially related. We examine how nulls are created and annihilated during bifurcation processes, and describe how they evolve within the current layer. The type of null bifurcation first observed is associated with the formation of pairs of flux ropes within the current layer.more » We also find that new nulls form within these flux ropes, both following internal reconnection and as adjacent flux ropes interact. The flux ropes exhibit a complex evolution, driven by a combination of ideal kinking and their interaction with the outflow jets from the main layer. The finite size of the unstable layer also allows us to consider the wider effects of flux rope generation. We find that the unstable current layer acts as a source of torsional magnetohydrodynamic waves and dynamic braiding of magnetic fields. The implications of these results to several areas of heliophysics are discussed.« less

Interior Permanent Magnet Reluctance Machine with Brushless Field Excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiles, R.H.

2005-10-07

In a conventional permanent magnet (PM) machine, the air-gap flux produced by the PM is fixed. It is difficult to enhance the air-gap flux density due to limitations of the PM in a series-magnetic circuit. However, the air-gap flux density can be weakened by using power electronic field weakening to the limit of demagnetization of the PMs. This paper presents the test results of controlling the PM air-gap flux density through the use of a stationary brushless excitation coil in a reluctance interior permanent magnet with brushless field excitation (RIPM-BFE) motor. Through the use of this technology the air-gap fluxmore » density can be either enhanced or weakened. There is no concern with demagnetizing the PMs during field weakening. The leakage flux of the excitation coil through the PMs is blocked. The prototype motor built on this principle confirms the concept of flux enhancement and weakening through the use of excitation coils.« less

Witnessing magnetic twist with high-resolution observation from the 1.6-m New Solar Telescope

PubMed Central

Wang, Haimin; Cao, Wenda; Liu, Chang; Xu, Yan; Liu, Rui; Zeng, Zhicheng; Chae, Jongchul; Ji, Haisheng

2015-01-01

Magnetic flux ropes are highly twisted, current-carrying magnetic fields. They are crucial for the instability of plasma involved in solar eruptions, which may lead to adverse space weather effects. Here we present observations of a flaring using the highest resolution chromospheric images from the 1.6-m New Solar Telescope at Big Bear Solar Observatory, supplemented by a magnetic field extrapolation model. A set of loops initially appear to peel off from an overall inverse S-shaped flux bundle, and then develop into a multi-stranded twisted flux rope, producing a two-ribbon flare. We show evidence that the flux rope is embedded in sheared arcades and becomes unstable following the enhancement of its twists. The subsequent motion of the flux rope is confined due to the strong strapping effect of the overlying field. These results provide a first opportunity to witness the detailed structure and evolution of flux ropes in the low solar atmosphere. PMID:25919706

Analysis of Plasma Detachment through Magnetic Nozzle via Canonical Field Theory

NASA Astrophysics Data System (ADS)

Takagaki, Yu

In this paper, I have investigated the mechanism of plasma detachment through magnetic nozzle via canonical field theory, especially by considering canonical vorticity flux Psisigma contour and dissipative force vector Rsigma. As one of the most recent experimental proofs of plasma detachment, Olsen et al., observed and investigated three key indications of plasma detachment. However, after solving for numerical fits with their experimental data, I found that constant ion flux lines did not actually separate from constant magnetic flux lines. Thus, their first key indication becomes incorrect now. Whereas, my analytical results are consistent with the other two key indications. At the beginning, plasma detached from canonical vorticity flux contours due to non-zero dissipative force and attached on magnetic flux lines instead. However, vector Rsigma [is asymptotically equal to] 0 force makes plasma re-attach on canonical vorticity flux contours around the plume edge region. As the most significant and notable result through my analysis, I confirmed the existence of returning plasma flow around the plume edge region.

Traffic operational evaluation of traffic impact analysis (TIA) case sites.

DOT National Transportation Integrated Search

2010-09-22

This report summarizes traffic operational evaluation of six select traffic impact analysis (TIA) case sites and the effectiveness of forecasting methods used in TIA studies. Six TIA case sites comprising 15 signalized intersections and 2 unsignalize...

Empirically-based performance assessment & simulation of pedestrian behavior at unsignalized crossings.

DOT National Transportation Integrated Search

2014-09-01

The objective of this research was to provide an improved understanding of pedestrian-vehicle interaction : at mid-block pedestrian crossings and develop methods that can be used in traffic operational analysis and : microsimulation packages. Models ...

DNS Rebinding Attacks

DTIC Science & Technology

2009-09-01

active scripting, file downloads, installation of desktop items, signed and unsigned ActiveX controls, Java permissions, launching applications and...files in an IFRAME, running ActiveX controls and plug-ins, and scripting of Java applets [49]. This security measure is very effective against DNS

On the topology of flux transfer events

NASA Technical Reports Server (NTRS)

Hesse, Michael; Birn, Joachim; Schindler, Karl

1990-01-01

A topological analysis is made of a simple model magnetic field of a perturbation at the magnetopause that shares magnetic properties with flux transfer events. The aim is to clarify a number of topological aspects that arise in the case of fully three-dimensional magnetic fields. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause by the formation of a ropelike magnetic field structure. For this purpose a global topological model of a closed magnetosphere is considered as the unperturbed state. The topological substructure of the model flux rope is discussed in detail.

Flux density measurement of radial magnetic bearing with a rotating rotor based on fiber Bragg grating-giant magnetostrictive material sensors.

PubMed

Ding, Guoping; Zhang, Songchao; Cao, Hao; Gao, Bin; Zhang, Biyun

2017-06-10

The rotational magnetic field of radial magnetic bearings characterizes remarkable time and spatial nonlinearity due to the eddy current and induced electromagnetic field. It is significant to experimentally obtain the features of the rotational magnetic field of the radial magnetic bearings to validate the theoretical analysis and reveal the discipline of a rotational magnetic field. This paper developed thin-slice fiber Bragg grating-giant magnetostrictive material (FBG-GMM) magnetic sensors to measure air-gap flux density of a radial magnetic bearing with a rotating rotor; a radial magnetic bearing test rig was constructed and the rotational magnetic field with different rotation speed was measured. Moreover, the finite element method (FEM) was used to simulate the rotational magnetic field; the measurement results and FEM results were investigated, and it was concluded that the FBG-GMM sensors were capable of measuring the radial magnetic bearing's air gap flux density with a rotating rotor, and the measurement results showed a certain degree of accuracy.

Observation of a commensurate array of flux chains in tilted flux lattices in Bi-Sr-Ca-Cu-O single crystals

NASA Astrophysics Data System (ADS)

Bolle, C. A.; Gammel, P. L.; Grier, D. G.; Murray, C. A.; Bishop, D. J.; Mitzi, D. B.; Kapitulnik, A.

1991-01-01

We report the observation of a novel flux-lattice structure, a commensurate array of flux-line chains. Our experiments consist of the magnetic decoration of the flux lattices in single crystals of Ba-Sr-Ca-Cu-O where the magnetic field is applied at an angle with respect to the conducting planes. For a narrow range of angles, the equilibrium structure is one with uniformly spaced chains with a higher line density of vortices than the background lattice. Our observations are in qualitative agreement with theories which suggest that, in strongly anisotropic materials the vortices develop an attractive interaction in tilted magnetic fields.

Thermal Evolution of a Failed Flux Rope Eruption Revealed by Temperature Maps

NASA Astrophysics Data System (ADS)

Song, H.; Zhang, J.; CHEN, Y.

2013-12-01

Flux rope is generally considered to be the fundamental magnetic configuration of a coronal mass ejection (CME). Recent observations suggest that hot channel or blob structures during the eruptions be the direct observational manifestation of flux ropes. In this study, we report our analysis of thermal evolution of a failed solar eruption with an apparent flux rope embedded. The thermal structure of the eruption is revealed through differential emission measure (DEM) analysis technique, which shows detailed temperature maps in both high spatial resolution and high temperature resolution based on SDO/AIA observations. Our results show that the flux rope exists in the corona before the eruption, and its temperature can quickly rise to over 10 MK within one minute of the eruption. The correlation study between the flux rope temperature and the soft x-ray flux suggests that the flux rope should be heated through the direct thermal energy release of magnetic reconnection. Further, we study the kinematic evolution process of the flux rope, in an effort to find the physical mechanism that prevents the magnetic rope eruption to become a full coronal mass ejection. This kind of study using temperature maps might reveal where and when magnetic reconnection takes place during solar eruptions.

Observations of Magnetic Evolution and Network Flares Driven by Photospheric Flows in the Quiet Sun

NASA Astrophysics Data System (ADS)

Attie, Raphael; Thompson, Barbara J.

2017-08-01

The quiet Sun may be the biggest laboratory to study physical elementary processes of fundamental importance to space plasma. The advantage is the continuous availability of small-scale events, carrying the hidden microphysics that is responsible for larger-scale phenomena. By small-scale events, we mean spatial dimensions of a few Mm at most, and durations of less than an hour. I present here an attempt to describe and understand the coupling between the photospheric flows, the photospheric magnetic flux, and small-scale energetic transient events. By adapting and improving the highly efficient Balltracking technique for Hinode/SOT data, we relate the fine structures of the supergranular flow fields with the magnetic flux evolution. For studying the dynamics of the latter, and more precisely, the magnetic flux cancellation at sites of energy releases, we applied a new feature tracking algorithm called "Magnetic Balltracking" -- which tracks photospheric magnetic elements -- to high-resolution magnetograms from Hinode/SOT.Using observations of the low corona in soft X-rays with Hinode/XRT, we analyse the triggering mechanism of small-scale network flares. By tracking both the flow fields on the one hand, and the magnetic motions on the other hand, we relate the flows with cancelling magnetic flux. We identify two patterns of horizontal flows that act as catalysts for efficient magnetic reconnection: (i) Funnel-shaped streamlines in which the magnetic flux is carried, and (ii) large-scale vortices (~10 Mm and above) at the network intersections, in which distant magnetic features of opposite polarities seem to be sucked in and ultimately vanish. The excess energy stored in the stressed magnetic field of the vortices is sufficient to power network flares.Prospects for determining the magnetic energy budget in the quiet sun are discussed.

Study of an expanding magnetic cloud

NASA Astrophysics Data System (ADS)

Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P.

Magnetic Clouds (MCs) transport into the interplanetary medium the magnetic flux and helicity released in coronal mass ejections by the Sun. At 1 AU from the Sun, MCs are generally modelled as static flux ropes. However, the velocity profile of some MCs presents signatures of expansion. We analise here the magnetic structure of an expanding magnetic cloud observed by Wind spacecraft. We consider a dynamical model, based on a self-similar behaviour for the cloud radial velocity. We assume a free expansion for the cloud, and a cylindrical linear force free field (i.e., the Lundquist's field) as the initial condition for its magnetic configuration. We derive theoretical expressions for the magnetic flux across a surface perpendicular to the cloud axis, for the magnetic helicity and magnetic energy per unit length along the tube using the self-similar model. Finally, we compute these magntitudes with the fitted parameters. FULL TEXT IN SPANISH

GENESIS OF INTERPLANETARY INTERMITTENT TURBULENCE: A CASE STUDY OF ROPE–ROPE MAGNETIC RECONNECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chian, Abraham C.-L.; Loew, Murray H.; Feng, Heng Q.

In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad–Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope–rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event.more » The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.« less

Placed in a steady magnetic field, the flux density inside a permalloy-shielded volume decreases over hours and days

NASA Astrophysics Data System (ADS)

Feinberg, Benedict; Gould, Harvey

2018-03-01

Following the application of an external magnetic field to a thin-walled demagnetized Permalloy cylinder, the magnetic flux density at the center of the shielded volume decreases by roughly 20% over periods of hours to days. We measured this effect for applied magnetic fields from 0.48 A/m to 16 A/m, the latter being comparable to the Earths magnetic field at its weakest point. Delayed changes in magnetic flux density are also observed following alternating current demagnetization. We attribute these effects to delayed changes in magnetization, which have previously been observed in thin Permalloy films and small bulk samples of ferromagnetic materials. Phenomenological models of thermal activation are discussed. Some possible effects on experiments that rely on static shielding are noted.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Requerey, Iker S.; Cobo, B. Ruiz; Iniesta, J. C. Del Toro

We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe i line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarities and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footpoint is weakermore » (1100 G) and displays an upflow, while the negative polarity footpoint is stronger (2200 G) and shows a downflow. This configuration is naturally interpreted as a siphon flow along an arched magnetic flux tube.« less

Development of dual field magnetic flux leakage (MFL) inspection technology to detect mechanical damage.

DOT National Transportation Integrated Search

2013-03-01

This report details the development and testing of a dual magnetization in-line inspection (ILI) : tool for detecting mechanical damage in operating pipelines, including the first field trials of a : fully operational dual-field magnetic flux leakage...

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films

NASA Technical Reports Server (NTRS)

Xing, W.; Heinrich, B.; Zhou, HU; Fife, A. A.; Cragg, A. R.; Grant, P. D.

1995-01-01

Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown.

Optimization of Magneto-Rheological Damper for Maximizing Magnetic Flux Density in the Fluid Flow Gap Through FEA and GA Approaches

NASA Astrophysics Data System (ADS)

Krishna, Hemanth; Kumar, Hemantha; Gangadharan, Kalluvalappil

2017-08-01

A magneto rheological (MR) fluid damper offers cost effective solution for semiactive vibration control in an automobile suspension. The performance of MR damper is significantly depends on the electromagnetic circuit incorporated into it. The force developed by MR fluid damper is highly influenced by the magnetic flux density induced in the fluid flow gap. In the present work, optimization of electromagnetic circuit of an MR damper is discussed in order to maximize the magnetic flux density. The optimization procedure was proposed by genetic algorithm and design of experiments techniques. The result shows that the fluid flow gap size less than 1.12 mm cause significant increase of magnetic flux density.

Kinetic Simulations of Plasma Energization and Particle Acceleration in Interacting Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Du, S.; Guo, F.; Zank, G. P.; Li, X.; Stanier, A.

2017-12-01

The interaction between magnetic flux ropes has been suggested as a process that leads to efficient plasma energization and particle acceleration (e.g., Drake et al. 2013; Zank et al. 2014). However, the underlying plasma dynamics and acceleration mechanisms are subject to examination of numerical simulations. As a first step of this effort, we carry out 2D fully kinetic simulations using the VPIC code to study the plasma energization and particle acceleration during coalescence of two magnetic flux ropes. Our analysis shows that the reconnection electric field and compression effect are important in plasma energization. The results may help understand the energization process associated with magnetic flux ropes frequently observed in the solar wind near the heliospheric current sheet.

The deformation of flux tubes in the solar wind with applications to the structure of magnetic clouds and CMEs

NASA Technical Reports Server (NTRS)

Cargill, Peter J.; Chen, James; Spicer, D. S.; Zalesak, S. T.

1994-01-01

Two dimensional magnetohydrodynamic simulations of the distortion of a magnetic flux tube, accelerated through ambient solar wind plasma, are presented. Vortices form on the trailing edge of the flux tube, and couple strongly to its interior. If the flux tube azimuthal field is weak, it deforms into an elongated banana-like shape after a few Alfven transit times. A significant azimuthal field component inhibits this distortion. In the case of magnetic clouds in the solar wind, it is suggested that the shape observed at 1 AU was determined by distortion of the cloud in the inner heliosphere. Distortion of the cloud beyond 1 AU takes many days. It is estimated that effective drag coefficients slightly greater than unity are appropriate for modeling flux tube propagation. Synthetic magnetic field profiles as would be seen by a spacecraft traversing the cloud are presented.

High temperature superconductor dc-SQUID microscope with a soft magnetic flux guide

NASA Astrophysics Data System (ADS)

Poppe, U.; Faley, M. I.; Zimmermann, E.; Glaas, W.; Breunig, I.; Speen, R.; Jungbluth, B.; Soltner, H.; Halling, H.; Urban, K.

2004-05-01

A scanning SQUID microscope based on high-temperature superconductor (HTS) dc-SQUIDs was developed. An extremely soft magnetic amorphous foil was used to guide the flux from room temperature samples to the liquid-nitrogen-cooled SQUID sensor and back. The flux guide passes through the pick-up loop of the HTS SQUID, providing an improved coupling of magnetic flux of the object to the SQUID. The device measures the z component (direction perpendicular to the sample surface) of the stray field of the sample, which is rastered with submicron precision in the x-y direction by a motorized computer-controlled scanning stage. A lateral resolution better than 10 µm, with a field resolution of about 0.6 nT Hz-1/2 was achieved for the determination of the position of the current carrying thin wires. The presence of the soft magnetic foil did not significantly increase the flux noise of the SQUID.

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, C.; Fabbian, D.; Rezaei, R.

2017-06-10

Before using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on themore » basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112, and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS), and the GREGOR Fabry–Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet-Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS, and GFPI observations.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Bo; Jiang, Yunchun; Yang, Jiayan

Taking advantage of the high spatiotemporal resolution observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we present rare observations of the rapid formation of a filament caused by magnetic reconnection between two sets of dark threadlike structures. The two sets of dark threadlike structures belong to distinct flux systems with their adjacent ends anchored in an opposite-polarity magnetic field region, where the calculated photospheric velocity field shows that converging flows dominate there. Due to the converging flows, opposite-polarity magnetic flux converged and then canceled, leading to the formation ofmore » extreme ultraviolet (EUV) brightening that spread in opposite directions along the spine of the dark threadlike structures. Meanwhile, very weak remote brightening in the other terminals of the dark threadlike structures, as well as EUV loops, which rooted in the opposite-polarity magnetic field region, appeared. In addition, all of the AIA Fe line observations reveal that a flux rope was formed and underwent a rolling motion during the fadeaway of the EUV brightening. Soon after, as the EUV brightening disappeared, a filament that is very likely composed of two sets of intertwined dark threadlike structures was formed. Via differential emission measure (EM) analysis, it is found that both the EM and temperature of the plasma around the flux-canceling site increased during the brightening, implying that there, magnetic reconnection may occur to heat the plasma. These observations provide evidence that the filament is formed by magnetic reconnection associated with flux convergence and cancellation, and the magnetic structure of the filament is most likely a flux rope.« less

CIR-XL recurring for several years

NASA Astrophysics Data System (ADS)

Dósa, Melinda; Erdös, Géza

2016-04-01

The heliospheric magnetic flux is determined from the radial component of the magnetic field vector measured onboard interplanetary space probes. Earlier Ulysses research has shown remarkable independence of the flux from heliographic latitude. Here we are investigating whether any longitudinal variation exist in the 50 year long OMNI magnetic data set. When determining the heliographic longitude of the plasma source, correction was applied for the solar wind travel time. Significant recurrent enhancements of the magnetic flux was observed during the declining phase of the solar cycles. These flux enhancements are associated with co-rotating interaction regions (CIR) lasting several years. The recurrence period is slightly faster than the Carrington Rotation rate. The same, long lasting recurring features can be observed when plotting the deviation angle of the solar wind velocity vector from the radial direction. However, the deviation angle is small - in order of a few degrees - and cannot account for the observed flux increases. An increase of the magnetic field is clearly caused by the plasma compression associated to CIRs. Comparing interplanetary data with synoptic maps of the coronal magnetic field (PFSS modell) and coronal temperature data of ACE, we came to the possible explanation that these long-term structures are caused by fast speed solar wind originating from coronal holes. This results supports the idea that magnetic field lines from coronal holes spread out and reach to low latitudes as well. The recurrent longitudinal variation of the magnetic flux during the declining phase of the solar cycle has impact on the modulation of cosmic rays as well as on the frequency and intensity of space weather events.

Directed flux motor

NASA Technical Reports Server (NTRS)

Wilson, Andrew (Inventor); Punnoose, Andrew (Inventor); Strausser, Katherine (Inventor); Parikh, Neil (Inventor)

2011-01-01

A directed flux motor described utilizes the directed magnetic flux of at least one magnet through ferrous material to drive different planetary gear sets to achieve capabilities in six actuated shafts that are grouped three to a side of the motor. The flux motor also utilizes an interwoven magnet configuration which reduces the overall size of the motor. The motor allows for simple changes to modify the torque to speed ratio of the gearing contained within the motor as well as simple configurations for any number of output shafts up to six. The changes allow for improved manufacturability and reliability within the design.

Dual-keel electrodynamic maglev system

DOEpatents

He, J.L.; Wang, Z.; Rote, D.M.; Coffey, H.T.; Hull, J.R.; Mulcahy, T.M.; Cal, Y.

1996-12-24

A propulsion and stabilization system is disclosed with a plurality of superconducting magnetic devices affixed to the dual-keels of a vehicle, where the superconducting magnetic devices produce a magnetic field when energized. The system also includes a plurality of figure-eight shaped null-flux coils affixed to opposing vertical sides of slots in a guideway. The figure-eight shaped null-flux coils are vertically oriented, laterally cross-connected in parallel, longitudinally connected in series, and continue the length of the vertical slots providing levitation and guidance force. An external power source energizes the figure-eight shaped null-flux coils to create a magnetic traveling wave that interacts with the magnetic field produced by the superconducting magnets to impart motion to the vehicle. 6 figs.

Influence of the interaction between the inter- and intragranular magnetic responses in the analysis of the ac susceptibility of a granular FeSe0.5Te0.5 superconductor

NASA Astrophysics Data System (ADS)

Mancusi, D.; Polichetti, M.; Cimberle, M. R.; Pace, S.

2015-09-01

The temperature-dependent fundamental ac susceptibility of a granular superconductor in the absence of dc fields has been analyzed by developing a phenomenological model for effective magnetic fields, taking into account the influence of the magnetic interaction between the intergranular and the intragranular magnetizations due to demagnetizing effects. For this purpose a policrystal Fe-based superconductor FeSe0.5Te0.5 sample has been studied. By the frequency dependence of the peaks of the temperature-dependent imaginary part of the fundamental complex susceptibility, the dependence on temperature of the characteristic times both for intergranular and intragranular relaxations of magnetic flux are derived, and the corresponding relaxation processes due to combinations of the flux creep, the flux flow and the thermally activated flux flow regimes are identified on the basis of the effective magnetic fields both at the sample surface and at the grains’ surfaces. Such characteristic times, through the Havriliak-Negami function, determine the temperature and the frequency dependences of the complex susceptibility. The comparison of the numerically obtained curves with the experimental ones confirms the relevance, for identifying the intergranular and intragranular contributions to the ac magnetic response and the corresponding flux dynamical regimes, of the interaction between the intergranular and intragranular magnetizations due to demagnetizing effects.

Magnetic flux trapping during field reversal in the formation of a field-reversed configuration

NASA Astrophysics Data System (ADS)

Steinhauer, Loren C.

1985-11-01

The flow of plasma and magnetic flux toward a wall is examined in a slab geometry where the magnetic field is parallel to the wall. Magnetohydrodynamic (MHD) flow with a quasisteady approximation is assumed that reduces the problem to three coupled ordinary differential equations. The calculated behavior shows that a thin current sheath is established at the wall in which a variety of phenomena appear, including significant resistive heating and rapid deceleration of the plasma flow. The sheath physics determines the speed at which flux and plasma flow toward the wall. The model has been applied to the field-reversal phase of a field-reversed theta pinch, during which the reduced magnetic field near the wall drives an outward flow of plasma and magnetic flux. The analysis leads to approximate expressions for the instantaneous flow speed, the loss of magnetic flux during the field reversal phase, the integrated heat flow to the wall, and the highest possible magnetic flux retained after reversal. Predictions from this model are compared with previous time-dependent MHD calculations and with experimental results from the TRX-1 [Proceedings of the 4th Symposium on the Physics and Technology of Compact Toroids, 27-29 October 1981 (Lawrence Livermore National Laboratory, Livermore, CA, 1982), p. 61] and TRX-2 [Proceedings of the 6th U.S. Symposium on Compact Toroid Research, 20-23 February, 1984 (Princeton Plasma Physics Laboratory, Princeton, NJ, 1984), p. 154] experiments.

The magnitude of the magnetic field near the surface of a high-T(sub c) superconductor with a trapped flux

NASA Technical Reports Server (NTRS)

Overcash, Dan R.

1991-01-01

In 1986, much excitement was caused by the discovery of a class of materials that conducted electricity with zero resistance at temperatures above the boiling temperature of liquid nitrogen. This excitement was checked by the difficulties of manufacturing ceramics and the usefulness of high temperature superconductors that were restricted by their becoming high resistive conductors at small current densities. A lack of pinning of the magnetic field flux caused the return of high resistance as the current was increased in these materials. A study of the magnetic field near the surface of a high temperature superconductor is the first step in the search for a means of pinning the flux lines and increasing their critical current densities. The author found that a comparison between the defects in the surface of the superconductor and the magnetic field showed only a change in the field near the notch and the edge. No correlation was found between the surface grain or structure and the oscillations in the magnetic field. The observed changes in the magnetic field show resonances which may give an indication of the non-flux pinning in these superconductors. A flux pinning mechanism will increase the critical current densities; therefore, other methods of determining this field should be tried. The author proposes using a flux gate magnetometer with a detector wound on a ferrite core to measure the magnitude and direction of the magnetic field.

Design and analysis of a flux intensifying permanent magnet embedded salient pole wind generator

NASA Astrophysics Data System (ADS)

Guo, Yujing; Jin, Ping; Lin, Heyun; Yang, Hui; Lyu, Shukang

2018-05-01

This paper presents an improved flux intensifying permanent magnet embedded salient pole wind generator (FI-PMESPWG) with mirror symmetrical magnetizing directions permanent magnet (PM) for improving generator's performances. The air-gap flux densities, the output voltage, the cogging torque and the d- and q-axis inductances of FI-PMESPWG are all calculated and analyzed by using the finite element method (FEM). To highlight the advantages of the proposed FI-PMESPWG, an original permanent magnet embedded salient pole wind generator (PMESPWG) model is adopted for comparison under the same operating conditions. The calculating results show that the air-gap flux densities of FI-PMESPWG are intensified with the same magnet amounts because the PMs are set in a form of V shape in each pole. The difference between d-axis inductance and q-axis inductance of the proposed FI-PMESPWG is reduced. Thus, the output power of the proposed FI-PMESPWG reaches a higher value than that of the original PMESPWG at the same current phase angle. The cogging torque is diminished because the flux path is changed. All the analysis results indicate that the electromagnetic characteristics of the proposed FI-PMESPWG are significantly better than that of the original PMESPWG.

Magnetic flux and heat losses by diffusive, advective, and Nernst effects in MagLIF-like plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velikovich, A. L., E-mail: sasha.velikovich@nrl.navy.mil; Giuliani, J. L., E-mail: sasha.velikovich@nrl.navy.mil; Zalesak, S. T.

2014-12-15

The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot plasma to the cold liner is dominated by the transverse heat conduction and advection, andmore » the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ω{sub e}τ{sub e} effective diffusion coefficients determining the losses of heat and magnetic flux are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient, which is commonly associated with low collisionality and two-dimensional transport. This family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.« less

IS FLUX ROPE A NECESSARY CONDITION FOR THE PROGENITOR OF CORONAL MASS EJECTIONS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Y.; Yang, K.; Chen, P. F., E-mail: chenpf@nju.edu.cn

2015-12-10

A magnetic flux rope structure is believed to exist in most coronal mass ejections (CMEs). However, it has been long debated whether the flux rope exists before eruption or if it is formed during eruption via magnetic reconnection. The controversy has continued because of our lack of routine measurements of the magnetic field in the pre-eruption structure, such as solar filaments. However, recently an indirect method was proposed to infer the magnetic field configuration based on the sign of helicity and the bearing direction of the filament barbs. In this paper, we apply this method to two erupting filament events, one onmore » 2014 September 2 and the other on 2011 March 7, and find that the first filament is supported by a magnetic flux rope and the second filament is supported by a sheared arcade, i.e., the first one is an inverse-polarity filament and the second one is a normal-polarity filament. With the identification of the magnetic configurations in these two filaments, we stress that a flux rope is not a necessary condition for the pre-CME structure.« less

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

PubMed

Gao, Nuo; Zhu, S A; He, Bin

2005-06-07

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

MAGNETIC FLUX CANCELLATION IN ELLERMAN BOMBS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reid, A.; Mathioudakis, M.; Nelson, C. J.

2016-06-01

Ellerman Bombs (EBs) are often found to be co-spatial with bipolar photospheric magnetic fields. We use H α imaging spectroscopy along with Fe i 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope (SST), combined with data from the Solar Dynamic Observatory , to study EBs and the evolution of the local magnetic fields at EB locations. EBs are found via an EB detection and tracking algorithm. Using NICOLE inversions of the spectropolarimetric data, we find that, on average, (3.43 ± 0.49) × 10{sup 24} erg of stored magnetic energy disappears from the bipolar region during EB burning. Themore » inversions also show flux cancellation rates of 10{sup 14}–10{sup 15} Mx s{sup −1} and temperature enhancements of 200 K at the detection footpoints. We investigate the near-simultaneous flaring of EBs due to co-temporal flux emergence from a sunspot, which shows a decrease in transverse velocity when interacting with an existing, stationary area of opposite polarity magnetic flux, resulting in the formation of the EBs. We also show that these EBs can be fueled further by additional, faster moving, negative magnetic flux regions.« less

Magnetic flux ropes in the Venus ionosphere - Observations and models

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Russell, C. T.

1983-01-01

Pioneer Venus Orbiter data are used as evidence of naturally occurring magnetic field filamentary structures which can be described by a flux rope model. The solar wind is interpreted as piling up a magnetic field on the Venus ionosphere, with the incident ram pressure being expressed as magnetic field pressure. Currents flowing at the ionopause shield out the field, allowing magnetic excursions to be observed with magnitudes of tens of nT over an interval of a few seconds. A quantitative assessment is made of the signature expected from a flux rope. It is noted that each excursion of the magnetic field detected by the Orbiter magnetometer was correlated with variations in the three components of the field. A coordinate system is devised which shows that the Venus data is indicative of the presence of flux ropes whose parameters are the coordinates of the system and would yield the excursions observed in the spacecraft crossings of the fields.

Guiding thermomagnetic avalanches with soft magnetic stripes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlasko-Vlasov, V. K.; Colauto, F.; Benseman, T.

We demonstrate the potential for manipulating the ultrafast dynamics of thermomagnetic flux avalanches (TMA) in superconducting films with soft magnetic stripes deposited on the film. By tuning the in-plane magnetization of the stripes, we induce lines of strong magnetic potentials for Abrikosov vortices, resulting in guided slow motion of vortices along the stripe edges and preferential bursts of TMA along the stripes. Furthermore, we show that transversely polarized stripes can reduce the TMA size by diverting magnetic flux away from the major trunk of the TMA into interstripe gaps. Our data indicate that TMAs are launched from locations with enhancedmore » vortex entry barrier, where flux accumulation followed by accelerated vortex discharge significantly reduces the threshold of the applied field ramping speed required for the creation of TMAs. Finally, vortex-antivortex annihilation at the moving front of an expanding TMA can account for the enhanced TMA activity in the receding branches of the sample's magnetization cycle and the preferred propagation of TMAs into maximum trapped flux regions.« less

Guiding thermomagnetic avalanches with soft magnetic stripes

NASA Astrophysics Data System (ADS)

Vlasko-Vlasov, V. K.; Colauto, F.; Benseman, T.; Rosenmann, D.; Kwok, W.-K.

2017-12-01

We demonstrate the potential for manipulating the ultrafast dynamics of thermomagnetic flux avalanches (TMA) in superconducting films with soft magnetic stripes deposited on the film. By tuning the in-plane magnetization of the stripes, we induce lines of strong magnetic potentials for Abrikosov vortices, resulting in guided slow motion of vortices along the stripe edges and preferential bursts of TMA along the stripes. Furthermore, we show that transversely polarized stripes can reduce the TMA size by diverting magnetic flux away from the major trunk of the TMA into interstripe gaps. Our data indicate that TMAs are launched from locations with enhanced vortex entry barrier, where flux accumulation followed by accelerated vortex discharge significantly reduces the threshold of the applied field ramping speed required for the creation of TMAs. Finally, vortex-antivortex annihilation at the moving front of an expanding TMA can account for the enhanced TMA activity in the receding branches of the sample's magnetization cycle and the preferred propagation of TMAs into maximum trapped flux regions.

The Formation of Magnetic Depletions and Flux Annihilation Due to Reconnection in the Heliosheath

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drake, J. F.; Swisdak, M.; Opher, M.

The misalignment of the solar rotation axis and the magnetic axis of the Sun produces a periodic reversal of the Parker spiral magnetic field and the sectored solar wind. The compression of the sectors is expected to lead to reconnection in the heliosheath (HS). We present particle-in-cell simulations of the sectored HS that reflect the plasma environment along the Voyager 1 and 2 trajectories, specifically including unequal positive and negative azimuthal magnetic flux as seen in the Voyager data. Reconnection proceeds on individual current sheets until islands on adjacent current layers merge. At late time, bands of the dominant fluxmore » survive, separated by bands of deep magnetic field depletion. The ambient plasma pressure supports the strong magnetic pressure variation so that pressure is anticorrelated with magnetic field strength. There is little variation in the magnetic field direction across the boundaries of the magnetic depressions. At irregular intervals within the magnetic depressions are long-lived pairs of magnetic islands where the magnetic field direction reverses so that spacecraft data would reveal sharp magnetic field depressions with only occasional crossings with jumps in magnetic field direction. This is typical of the magnetic field data from the Voyager spacecraft. Voyager 2 data reveal that fluctuations in the density and magnetic field strength are anticorrelated in the sector zone, as expected from reconnection, but not in unipolar regions. The consequence of the annihilation of subdominant flux is a sharp reduction in the number of sectors and a loss in magnetic flux, as documented from the Voyager 1 magnetic field and flow data.« less

Roadway lighting and safety : phase II--monitoring quality, durability and efficiency.

DOT National Transportation Integrated Search

2011-10-01

This Phase II project follows a previous project titled Strategies to Address Nighttime Crashes at Rural, Unsignalized Intersections. Based on the results of the previous study, the Iowa Highway Research Board (IHRB) indicated interest in pursuing fu...

Power flow control using distributed saturable reactors

DOEpatents

Dimitrovski, Aleksandar D.

2016-02-13

A magnetic amplifier includes a saturable core having a plurality of legs. Control windings wound around separate legs are spaced apart from each other and connected in series in an anti-symmetric relation. The control windings are configured in such a way that a biasing magnetic flux arising from a control current flowing through one of the plurality of control windings is substantially equal to the biasing magnetic flux flowing into a second of the plurality of control windings. The flow of the control current through each of the plurality of control windings changes the reactance of the saturable core reactor by driving those portions of the saturable core that convey the biasing magnetic flux in the saturable core into saturation. The phasing of the control winding limits a voltage induced in the plurality of control windings caused by a magnetic flux passing around a portion of the saturable core.

Understanding the Twist Distribution Inside Magnetic Flux Ropes by Anatomizing an Interplanetary Magnetic Cloud

NASA Astrophysics Data System (ADS)

Wang, Yuming; Shen, Chenglong; Liu, Rui; Liu, Jiajia; Guo, Jingnan; Li, Xiaolei; Xu, Mengjiao; Hu, Qiang; Zhang, Tielong

2018-05-01

Magnetic flux rope (MFR) is the core structure of the greatest eruptions, that is, the coronal mass ejections (CMEs), on the Sun, and magnetic clouds are posteruption MFRs in interplanetary space. There is a strong debate about whether or not a MFR exists prior to a CME and how the MFR forms/grows through magnetic reconnection during the eruption. Here we report a rare event, in which a magnetic cloud was observed sequentially by four spacecraft near Mercury, Venus, Earth, and Mars, respectively. With the aids of a uniform-twist flux rope model and a newly developed method that can recover a shock-compressed structure, we find that the axial magnetic flux and helicity of the magnetic cloud decreased when it propagated outward but the twist increased. Our analysis suggests that the "pancaking" effect and "erosion" effect may jointly cause such variations. The significance of the pancaking effect is difficult to be estimated, but the signature of the erosion can be found as the imbalance of the azimuthal flux of the cloud. The latter implies that the magnetic cloud was eroded significantly leaving its inner core exposed to the solar wind at far distance. The increase of the twist together with the presence of the erosion effect suggests that the posteruption MFR may have a high-twist core enveloped by a less-twisted outer shell. These results pose a great challenge to the current understanding on the solar eruptions as well as the formation and instability of MFRs.

The Cosmic Battery Revisited

NASA Technical Reports Server (NTRS)

Contopoulos, Ioannis; Kazanas, Demosthenes; Christodoulos, Dimistris M.

2007-01-01

We reinvestigate the generation and accumulation of magnetic flux in optically thin accretion flows around active gravitating objects. The source of the magnetic field is the azimuthal electric current associated with the Poynting-Robertson drag on the electrons of the accreting plasma. This current generates magnetic field loops which open up because of the differential rotation of the flow. We show through simple numerical simulations that what regulates the generation and accumulation of magnetic flux near the center is the value of the plasma conductivity. Although the conductivity is usually considered to be effectively infinite for the fully ionized plasmas expected near the inner edge of accretion disks, the turbulence of those plasmas may actually render them much less conducting due to the presence of anomalous resistivity. We have discovered that if the resistivity is sufficiently high throughout the turbulent disk while it is suppressed interior to its inner edge, an interesting steady-state process is established: accretion carries and accumulates magnetic flux of one polarity inside the inner edge of the disk, whereas magnetic diffusion releases magnetic flux of the opposite polarity to large distances. In this scenario, magnetic flux of one polarity grows and accumulates at a steady rate in the region inside the inner edge and up to the point of equipartition when it becomes dynamically important. We argue that this inward growth and outward expulsion of oppositely-directed magnetic fields that we propose may account for the approx. 30 min cyclic variability observed in the galactic microquasar GRS1915+105.

Evolution of heliospheric magnetized configurations via topological invariants

NASA Astrophysics Data System (ADS)

Roth, Ilan

2013-07-01

The analogy between magnetohydrodynamics (MHD) and knot theory is utilized in presenting a new method for an analysis of stability and evolution of complex magnetic heliospheric flux tubes. Planar projection of a three-dimensional magnetic configuration depicts the structure as a two-dimensional diagram with crossings, to which one may assign mathematical operations leading to robust topological invariants. These invariants enrich the topological information of magnetic configurations beyond helicity. It is conjectured that the field which emerges from the solar photosphere is structured as one of the simplest knots-unknot or prime knot-and these flux ropes are then stretched while carried by the solar wind into the interplanetary medium. Preservation of invariants for small diffusivity and large cross section of the emerging magnetic flux makes them impervious to large scale reconnection, allowing us to predict the observed structures at 1 AU as elongated prime knots. Similar structures may be observed in magnetic clouds which got disconnected from their footpoints and in ion drop-out configurations from a compact flare source in solar impulsive solar events. Observation of small scale magnetic features consistent with prime knots may indicate spatial intermittency and non-Gaussian statistics in the turbulent cascade process. For flux tubes with higher resistivity, magnetic energy decay rate should decrease with increased knot complexity as the invariants are then harder to be violated. These observations could be confirmed if adjacent satellites happen to measure distinctly oriented magnetic fields with directionally varying suprathermal particle fluxes.

Magnetic flux and heat losses by diffusive, advective, and Nernst effects in magnetized liner inertial fusion-like plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.

The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstratesmore » that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.« less

Flux canceling in three-dimensional radiative magnetohydrodynamic simulations

NASA Astrophysics Data System (ADS)

Thaler, Irina; Spruit, H. C.

2017-05-01

We aim to study the processes involved in the disappearance of magnetic flux between regions of opposite polarity on the solar surface using realistic three-dimensional (3D) magnetohydrodynamic (MHD) simulations. "Retraction" below the surface driven by magnetic forces is found to be a very effective mechanism of flux canceling of opposite polarities. The speed at which flux disappears increases strongly with initial mean flux density. In agreement with existing inferences from observations we suggest that this is a key process of flux disappearance within active complexes. Intrinsic kG strength concentrations connect the surface to deeper layers by magnetic forces, and therefore the influence of deeper layers on the flux canceling process is studied. We do this by comparing simulations extending to different depths. For average flux densities of 50 G, and on length scales on the order of 3 Mm in the horizontal and 10 Mm in depth, deeper layers appear to have only a mild influence on the effective rate of diffusion.

3D-Printed Detector Band for Magnetic Off-Plane Flux Measurements in Laminated Machine Cores

PubMed Central

Pfützner, Helmut; Palkovits, Martin; Windischhofer, Andreas; Giefing, Markus

2017-01-01

Laminated soft magnetic cores of transformers, rotating machines etc. may exhibit complex 3D flux distributions with pronounced normal fluxes (off-plane fluxes), perpendicular to the plane of magnetization. As recent research activities have shown, detections of off-plane fluxes tend to be essential for the optimization of core performances aiming at a reduction of core losses and of audible noise. Conventional sensors for off-plane flux measurements tend to be either of high thickness, influencing the measured fluxes significantly, or require laborious preparations. In the current work, thin novel detector bands for effective and simple off-plane flux detections in laminated machine cores were manufactured. They are printed in an automatic way by an in-house developed 3D/2D assembler. The latter enables a unique combination of conductive and non-conductive materials. The detector bands were effectively tested in the interior of a two-package, three-phase model transformer core. They proved to be mechanically resilient, even for strong clamping of the core. PMID:29257063

3D-Printed Detector Band for Magnetic Off-Plane Flux Measurements in Laminated Machine Cores.

PubMed

Shilyashki, Georgi; Pfützner, Helmut; Palkovits, Martin; Windischhofer, Andreas; Giefing, Markus

2017-12-19

Laminated soft magnetic cores of transformers, rotating machines etc. may exhibit complex 3D flux distributions with pronounced normal fluxes (off-plane fluxes), perpendicular to the plane of magnetization. As recent research activities have shown, detections of off-plane fluxes tend to be essential for the optimization of core performances aiming at a reduction of core losses and of audible noise. Conventional sensors for off-plane flux measurements tend to be either of high thickness, influencing the measured fluxes significantly, or require laborious preparations. In the current work, thin novel detector bands for effective and simple off-plane flux detections in laminated machine cores were manufactured. They are printed in an automatic way by an in-house developed 3D/2D assembler. The latter enables a unique combination of conductive and non-conductive materials. The detector bands were effectively tested in the interior of a two-package, three-phase model transformer core. They proved to be mechanically resilient, even for strong clamping of the core.

Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

NASA Astrophysics Data System (ADS)

Liu, Chang; Fox, Will; Bhattacharjee, Amitava

2016-10-01

Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

Solar Active Region Coronal Jets. II. Triggering and Evolution of Violent Jets

NASA Astrophysics Data System (ADS)

Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Martinez, Francisco

2017-07-01

We study a series of X-ray-bright, rapidly evolving active region coronal jets outside the leading sunspot of AR 12259, using Hinode/X-ray telescope, Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI), and Interface Region Imaging Spectrograph (IRIS) data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets. The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ≲ 2\\prime\\prime ) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2016). Some jets strands are difficult/impossible to detect, perhaps due to, e.g., their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ˜ 1.5× {10}19 Mx hr-1. An average flux of ˜ 5× {10}18 Mx canceled prior to each episode, arguably building up ˜1028-1029 erg of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption build up and triggering of at least many jets in active regions, quiet regions, and coronal holes.

Surface flux transport simulations: Effect of inflows toward active regions and random velocities on the evolution of the Sun's large-scale magnetic field

NASA Astrophysics Data System (ADS)

Martin-Belda, D.; Cameron, R. H.

2016-02-01

Aims: We aim to determine the effect of converging flows on the evolution of a bipolar magnetic region (BMR), and to investigate the role of these inflows in the generation of poloidal flux. We also discuss whether the flux dispersal due to turbulent flows can be described as a diffusion process. Methods: We developed a simple surface flux transport model based on point-like magnetic concentrations. We tracked the tilt angle, the magnetic flux and the axial dipole moment of a BMR in simulations with and without inflows and compared the results. To test the diffusion approximation, simulations of random walk dispersal of magnetic features were compared against the predictions of the diffusion treatment. Results: We confirm the validity of the diffusion approximation to describe flux dispersal on large scales. We find that the inflows enhance flux cancellation, but at the same time affect the latitudinal separation of the polarities of the bipolar region. In most cases the latitudinal separation is limited by the inflows, resulting in a reduction of the axial dipole moment of the BMR. However, when the initial tilt angle of the BMR is small, the inflows produce an increase in latitudinal separation that leads to an increase in the axial dipole moment in spite of the enhanced flux destruction. This can give rise to a tilt of the BMR even when the BMR was originally aligned parallel to the equator.

Observation of the Meissner effect in a lattice Higgs model

NASA Technical Reports Server (NTRS)

Damgaard, Poul H.; Heller, Urs M.

1988-01-01

The lattice-regularized U(1) Higgs model in an external electromagnetic field is studied by Monte Carlo techniques. In the Coulomb phase, magnetic flux can flow through uniformly. The Higgs phase splits into a region where magnetic flux can penetrate only in the form of vortices and a region where the magnetic flux is completely expelled, the relativistic analog of the Meissner effect in superconductivity. Evidence is presented for symmetry restoration in strong external fields.

Magnetic flux transport and the sun's dipole moment - New twists to the Babcock-Leighton model

NASA Technical Reports Server (NTRS)

Wang, Y.-M.; Sheeley, N. R., Jr.

1991-01-01

The mechanisms that give rise to the sun's large-scale poloidal magnetic field are explored in the framework of the Babcock-Leighton (BL) model. It is shown that there are in general two quite distinct contributions to the generation of the 'alpha effect': the first is associated with the axial tilts of the bipolar magnetic regions as they erupt at the surface, while the second arises through the interaction between diffusion and flow as the magnetic flux is dispersed over the surface. The general relationship between flux transport and the BL dynamo is discussed.

Magnetic flux transport and the sun's dipole moment - New twists to the Babcock-Leighton model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y.-M.; Sheeley, N.R., Jr.

The mechanisms that give rise to the sun's large-scale poloidal magnetic field are explored in the framework of the Babcock-Leighton (BL) model. It is shown that there are in general two quite distinct contributions to the generation of the 'alpha effect': the first is associated with the axial tilts of the bipolar magnetic regions as they erupt at the surface, while the second arises through the interaction between diffusion and flow as the magnetic flux is dispersed over the surface. The general relationship between flux transport and the BL dynamo is discussed. 32 refs.

Topology optimization of reduced rare-earth permanent magnet arrays with finite coercivity

NASA Astrophysics Data System (ADS)

Teyber, R.; Trevizoli, P. V.; Christiaanse, T. V.; Govindappa, P.; Rowe, A.

2018-05-01

The supply chain risk of rare-earth permanent magnets has yielded research efforts to improve both materials and magnetic circuits. While a number of magnet optimization techniques exist, literature has not incorporated the permanent magnet failure process stemming from finite coercivity. To address this, a mixed-integer topology optimization is formulated to maximize the flux density of a segmented Halbach cylinder while avoiding permanent demagnetization. The numerical framework is used to assess the efficacy of low-cost (rare-earth-free ferrite C9), medium-cost (rare-earth-free MnBi), and higher-cost (Dy-free NdFeB) permanent magnet materials. Novel magnet designs are generated that produce flux densities 70% greater than the segmented Halbach array, albeit with increased magnet mass. Three optimization formulations are then explored using ferrite C9 that demonstrates the trade-off between manufacturability and design sophistication, generating flux densities in the range of 0.366-0.483 T.

Thermodynamics of Meissner effect and flux pinning behavior in the bulk of single-crystal La 2 - x Sr x CuO 4 ( x = 0.09 )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhiman, I.; Ziesche, R.; Anand, V. K.

We have studied the magnetic flux pinning behavior and Meissner effect for the high-more » $$T_{\\rm c}$$ single crystal La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($x$ = 0.09) superconductor using the polarized neutron imaging method with varying magnetic field and temperature. In the Meissner state expulsion of magnetic field (switched on during the measurements) is visualized, and the signatures of mixed state with increasing temperature are observed. While, for flux pinning behavior between 5 K $$\\leq$$ $T$ $$\\leq$$ 15 K and $$H_{\\rm ext}$$ = 63.5 mT (switched off during the measurements), the evolution of fringe pattern for both 0$$^{o}$$ and 90$$^{o}$$ sample orientation indicates magnetic flux pinning inside the bulk of the sample. At 25 K $$\\leq$$ $T$ $$\\leq$$ 32 K, a continuous decrease of inhomogeneously distribution pinned magnetic flux is observed, with the sample reaching a normal conducting state at $$T_{\\rm c}$$ ($$\\approx$$ 32 K). The flux pinning behavior is also explored as a function of $$H_{\\rm ext}$$, at $T$ = 5 K. As expected, with increasing $$H_{\\rm ext}$$ an increase in fringe density is observed, indicating an increase in magnetic flux pinning in the bulk of the sample. Therefore, in the present work for the first time we report bulk visualization of Meissner effect and flux pinning behavior in high-$$T_{\\rm c}$$ La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($x$ = 0.09) superconductor. This study clearly demonstrates the potential of real space polarized neutron imaging technique for the visualization of the superconducting mixed state, particularly in the field of high-$$T_{\\rm c}$$ superconductors.« less

Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings.

PubMed

Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R Matthew; Krishnan, Kannan M

2014-11-03

This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe 3 O 4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

Magnetic Reconnection Results on the Swarthmore Spheromak Experiment

NASA Astrophysics Data System (ADS)

Kornack, T. W.; Sollins, P. K.; Brown, M. R.

1997-11-01

Linear and 2D arrays of magnetic probes are used to study magnetic reconnection in the Swarthmore Spheromak Experiment (SSX). Opposing coaxial plasma guns form two identical spheromaks into adjacent 0.5 m diameter copper flux conservers. The flux conservers have symmetrical openings that allow the spheromaks to merge in a controlled manner. The stable equilibrium of the spheromaks provides a reservoir of magnetic flux for reconnection experiments. Currently, the magnetic configuration of the spheromaks allows the study of counter-helicity reconnection. Preliminary analysis will be presented and may include 2D B field movies of the reconnection region, measurement of the reconnection rate and comparison to the Sweet-Parker and standard Petschek models.

A Model of Coronal Streamers with Underlying Flux Ropes

NASA Astrophysics Data System (ADS)

Cottaar, M.; Fan, Y.

2009-10-01

We present global two-dimensional axisymmetric isothermal MHD simulations of the dynamic evolution of a coronal helmet streamer, driven at the lower boundary by the emergence of a twisted flux rope. By varying both the detached toroidal and poloidal fluxes emerged into the corona, but fixing the normal flux distribution at the surface at the end of the emergence, we obtain solutions that either settle to a new steady state of a stable helmet streamer containing a flux rope, or result in a disruption of the helmet with the underlying flux rope being expelled in a coronal mass ejection (CME)-like eruption. In all of the cases studied, we find that the transition from a stable to an eruptive state takes place at a magnetic energy that is very close to the Aly open field energy. Furthermore, we find that the transition from a stable to an eruptive end state does not occur at a single critical value of the total relative magnetic helicity, but depends on the profile of the underlying flux rope. Cases where the detached flux rope contains a higher amount of self-helicity, i.e., higher internal twist or detached poloidal flux, are found to become eruptive at a significantly lower total helicity. For the eruptive cases, the detached flux rope after emergence first rises quasi-statically due to a gradual opening of the field lines at the edge of the streamer and a slow reconnection below the flux rope, which continues to slowly increase the amount of the detached flux. This decreases the downward magnetic tension on the flux rope. The dynamic eruption is initiated when the magnetic pressure gradient no longer decreases fast enough to balance the decrease in the magnetic tension. Later rapid reconnections below the flux rope are important for accelerating the flux rope. For the stable helmets, we find that no cavities are formed due to the simplifying assumption of isothermal energetics and the uniform density lower boundary condition. However during the eruption we see the development of the 3-part structure of a CME.

Rotational magnetization: Problems in experimental and theoretical studies of electrical steels and amorphous magnetic materials

NASA Astrophysics Data System (ADS)

Moses, A. J.

1994-03-01

Flux rotating in the plane of laminations of amorphous materials or electrical steels can cause additional losses in electrical machines. To make full use of laboratory rotational magnetization studies, a better understanding of the nature of rotational flux in machine cores is needed. This paper highlights the need for careful laboratory simulation of the conditions which occur in actual machines. Single specimen tests must produce uniform flux over a given measuring region and output from field and flux sensors need careful analysis. Differences between thermal and flux sensing methods are shown as well as anomalies caused when the magnetisation direction is reversed in an anistropic specimen. Methods of overcoming these problems are proposed.

CURRENT SHEET THINNING AND ENTROPY CONSTRAINTS DURING THE SUBSTORM GROWTH PHASE

NASA Astrophysics Data System (ADS)

Otto, A.; Hall, F., IV

2009-12-01

A typical property during the growth phase of geomagnetic substorms is the thinning of the near-Earth current sheet, most pronounced in the region between 6 and 15 R_E. We propose that the cause for the current sheet thinning is convection from the midnight tail region to the dayside to replenish magnetospheric magnetic flux which is eroded at the dayside as a result of dayside reconnection. Adiabatic convection from the near-Earth tail region toward the dayside must conserve the entropy on magnetic field lines. This constraint prohibits a source of the magnetic flux from a region further out in the magnetotail. Thus the near-Earth tail region is increasingly depleted of magnetic flux (the Erickson and Wolf [1980] problem) with entropy matching that of flux tubes that are eroded on the dayside. It is proposed that the magnetic flux depletion in the near-Earth tail forces the formation of thin current layers. The process is documented by three-dimensional MHD simulations. It is shown that the simulations yield a time scale, location, and other general characteristics of the current sheet evolution during the substorm growth phase.

The Compound and Homologous Eruptions from the SAR 11429

NASA Astrophysics Data System (ADS)

Dhakal, Suman Kumar; Zhang, Jie

2016-05-01

Super Active Regions (SARs) are ARs which shows extremely high rate of solar eruptions. NOAA AR 11429 was a SAR which produced 47 C-Class, 15 M-Class and 3 X-Class flares and 8 CMEs during its passage from the front disk of the Sun. This SAR had anti-Hale and delta-spot magnetic configuration and many sub-regions of magnetic flux emergence. With the aid of multi-wavelength observations of the Solar Dynamics Observatory (SDO), the Solar Terrestrial Relations Observatory (STEREO) and nonlinear force-free model for the magnetic field in the solar corona, we found the existence of many magnetic flux structures (flux bundles) in the corona of the AR. The energy released by these co-existing flux bundles within short time, resulted in compound erutpions from the AR on March 9 and 10, 2012. In the period of 38 hours, after the CME eruption on March 9, the continuous shearing and cancellation and new magnetic flux emergence resulted in another CME on March 10. Both of the events showed the compound nature and the similarity of the foot-points and EUV dimming made these eruptions homologous.

Galactic Cosmic-Ray Anistropy During the Forbush Decrease Starting 2013 April 13

NASA Astrophysics Data System (ADS)

Tortermpun, U.; Ruffolo, D.; Bieber, J. W.

2018-01-01

The flux of Galactic cosmic rays (GCRs) can undergo a Forbush decrease (FD) during the passage of a shock, sheath region, or magnetic flux rope associated with a coronal mass ejection (CME). Cosmic-ray observations during FDs can provide information complementary to in situ observations of the local plasma and magnetic field, because cosmic-ray distributions allow remote sensing of distant conditions. Here we develop techniques to determine the GCR anisotropy before and during an FD using data from the worldwide network of neutron monitors, for a case study of the FD starting on 2013 April 13. We find that at times with strong magnetic fluctuations and strong cosmic-ray scattering, there were spikes of high perpendicular anisotropy and weak parallel anisotropy. In contrast, within the CME flux rope there was a strong parallel anisotropy in the direction predicted from a theory of drift motions into one leg of the magnetic flux rope and out the other, confirming that the anisotropy can remotely sense a large-scale flow of GCRs through a magnetic flux structure.

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, X., E-mail: xzm0005@auburn.edu; Maurer, D. A.; Knowlton, S. F.

2015-12-15

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used tomore » infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

NASA Astrophysics Data System (ADS)

Ma, X.; Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.

2015-12-01

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

DOE PAGES

Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ...

2015-12-22

Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is usedmore » to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

Theory of flux cutting and flux transport at the critical current of a type-II superconducting cylindrical wire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clem, John R

2011-02-17

I introduce a critical-state theory incorporating both flux cutting and flux transport to calculate the magnetic-field and current-density distributions inside a type-II superconducting cylinder at its critical current in a longitudinal applied magnetic field. The theory is an extension of the elliptic critical-state model introduced by Romero-Salazar and Pérez-Rodríguez. The vortex dynamics depend in detail on two nonlinear effective resistivities for flux cutting (ρ{sub ∥}) and flux flow (ρ{sub ⊥}), and their ratio r=ρ{sub ∥}/ρ{sub ⊥}. When r<1, the low relative efficiency of flux cutting in reducing the magnitude of the internal magnetic-flux density leads to a paramagnetic longitudinal magneticmore » moment. As a model for understanding the experimentally observed interrelationship between the critical currents for flux cutting and depinning, I calculate the forces on a helical vortex arc stretched between two pinning centers when the vortex is subjected to a current density of arbitrary angle Φ. Simultaneous initiation of flux cutting and flux transport occurs at the critical current density J{sub c}(Φ) that makes the vortex arc unstable.« less

Theory of flux cutting and flux transport at the critical current of a type-II superconducting cylindrical wire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clem, John R.

2011-02-17

I introduce a critical-state theory incorporating both flux cutting and flux transport to calculate the magnetic-field and current-density distributions inside a type-II superconducting cylinder at its critical current in a longitudinal applied magnetic field. The theory is an extension of the elliptic critical-state model introduced by Romero-Salazar and Perez-Rodriguez. The vortex dynamics depend in detail on two nonlinear effective resistivities for flux cutting ({rho}{parallel}) and flux flow ({rho}{perpendicular}), and their ratio r = {rho}{parallel}/{rho}{perpendicular}. When r < 1, the low relative efficiency of flux cutting in reducing the magnitude of the internal magnetic-flux density leads to a paramagnetic longitudinal magneticmore » moment. As a model for understanding the experimentally observed interrelationship between the critical currents for flux cutting and depinning, I calculate the forces on a helical vortex arc stretched between two pinning centers when the vortex is subjected to a current density of arbitrary angle {phi}. Simultaneous initiation of flux cutting and flux transport occurs at the critical current density J{sub c}({phi}) that makes the vortex arc unstable.« less

Dynamical onset of superconductivity and retention of magnetic fields in cooling neutron stars

NASA Astrophysics Data System (ADS)

Ho, Wynn C. G.; Andersson, Nils; Graber, Vanessa

2017-12-01

A superconductor of paired protons is thought to form in the core of neutron stars soon after their birth. Minimum energy conditions suggest magnetic flux is expelled from the superconducting region due to the Meissner effect, such that the neutron star core is largely devoid of magnetic fields for some nuclear equation of state and proton pairing models. We show via neutron star cooling simulations that the superconducting region expands faster than flux is expected to be expelled because cooling timescales are much shorter than timescales of magnetic field diffusion. Thus magnetic fields remain in the bulk of the neutron star core for at least 106-107yr . We estimate the size of flux free regions at 107yr to be ≲100 m for a magnetic field of 1011G and possibly smaller for stronger field strengths. For proton pairing models that are narrow, magnetic flux may be completely expelled from a thin shell of approximately the above size after 105yr . This shell may insulate lower conductivity outer layers, where magnetic fields can diffuse and decay faster, from fields maintained in the highly conducting deep core.

The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod

NASA Astrophysics Data System (ADS)

Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

2018-07-01

Management of power exhaust will be a crucial task for tokamak fusion reactors. Reactor concepts are often proposed with double-null divertors, i.e. having two magnetic separatrices in an up-down symmetric configuration. This arrangement is potentially advantageous since the majority of the tokamak exhaust power tends to flow to the outer pair of divertor legs at large major radius, where the geometry is favorable for spreading the heat over a large surface area and there is more room for advanced divertor configurations. Despite the importance, there have been relatively few studies of divertor power sharing in near double null configurations and no studies at the poloidal magnetic fields and scrape-off layer power widths anticipated for a reactor. Motivated by this need we have undertaken a systematic study on Alcator C-Mod, examining the effect of magnetic flux balance on the power sharing among the four divertor legs in near double-null plasmas. Ohmic L-modes at three values of plasma current and ICRF-heated enhanced D-alpha (EDA) H-modes and I-modes at a single value of plasma current are explored, producing poloidal magnetic fields of 0.42, 0.62 and 0.85 Tesla. For Ohmic L-modes and ICRF-heated EDA H-modes, we find that the point of equal power sharing between upper and lower divertors occurs remarkably close to a balanced double null. Power sharing amongst the outer (upper versus lower) and inner (upper versus lower) pairs of divertors can be described in terms of a logistic function of magnetic flux balance, consistent with heat flux mapping along magnetic field lines to the outer midplane. Power sharing between inner and outer legs is found to follow a Gaussian-like function of magnetic flux balance with non-zero power to the inner divertors at double null. The overall behavior of H-modes operated near double null and for I-modes operating to within one heat flux e-folding of double null are found similar to Ohmic L-modes, with a significant reduction of power on the inner divertor legs. The results are encapsulated in terms of empirically-informed analytic functions of magnetic flux balance. When combined with magnetic equilibrium control system specifications, these relationships can be used to specify the power flux handling requirements for each of the four divertor target plates.

Magnetic Flux Expulsion Studies in Niobium SRF Cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Posen, Sam; Checchin, Mattia; Crawford, Anthony

2016-06-01

With the recent discovery of nitrogen doping treatment for SRF cavities, ultra-high quality factors at medium accelerating fields are regularly achieved in vertical RF tests. To preserve these quality factors into the cryomodule, it is important to consider background magnetic fields, which can become trapped in the surface of the cavity during cooldown and cause Q₀ degradation. Building on the recent discovery that spatial thermal gradients during cooldown can significantly improve expulsion of magnetic flux, a detailed study was performed of flux expulsion on two cavities with different furnace treatments that are cooled in magnetic fields amplitudes representative of whatmore » is expected in a realistic cryomodule. In this contribution, we summarize these cavity results, in order to improve understanding of the impact of flux expulsion on cavity performance.« less

The Evolution of Open Magnetic Flux Driven by Photospheric Dynamics

NASA Technical Reports Server (NTRS)

Linker, Jon A.; Lionello, Roberto; Mikic, Zoran; Titov, Viacheslav S.; Antiochos, Spiro K.

2010-01-01

The coronal magnetic field is of paramount importance in solar and heliospheric physics. Two profoundly different views of the coronal magnetic field have emerged. In quasi-steady models, the predominant source of open magnetic field is in coronal holes. In contrast, in the interchange model, the open magnetic flux is conserved, and the coronal magnetic field can only respond to the photospheric evolution via interchange reconnection. In this view the open magnetic flux diffuses through the closed, streamer belt fields, and substantial open flux is present in the streamer belt during solar minimum. However, Antiochos and co-workers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet (HCS) - it will connect via narrow corridors to the polar coronal hole of the same polarity. This contradicts the requirements of the interchange model. We have performed an MHD simulation of the solar corona up to 20R solar to test both the interchange model and the Antiochos conjecture. We use a synoptic map for Carrington Rotation 1913 as the boundary condition for the model, with two small bipoles introduced into the region where a positive polarity extended coronal hole forms. We introduce flows at the photospheric boundary surface to see if open flux associated with the bipoles can be moved into the closed-field region. Interchange reconnection does occur in response to these motions. However, we find that the open magnetic flux cannot be simply injected into closed-field regions - the flux eventually closes down and disconnected flux is created. Flux either opens or closes, as required, to maintain topologically distinct open and closed field regions, with no indiscriminate mixing of the two. The early evolution conforms to the Antiochos conjecture in that a narrow corridor of open flux connects the portion of the coronal hole that is nearly detached by one of the bipoles. In the later evolution, a detached coronal hole forms, in apparent violation of the Antiochos conjecture. Further investigation reveals that this detached coronal hole is actually linked to the extended coronal hole by a separatrix footprint on the photosphere of zero width. Therefore, the essential idea of the conjecture is preserved, if we modify it to state that coronal holes in the same polarity region are always linked, either by finite width corridors or separatrix footprints. The implications of these results for interchange reconnection and the sources of the slow solar wind are briefly discussed.

The Evolution of Open Magnetic Flux Driven by Photospheric Dynamics

NASA Astrophysics Data System (ADS)

Linker, Jon A.; Lionello, Roberto; Mikić, Zoran; Titov, Viacheslav S.; Antiochos, Spiro K.

2011-04-01

The coronal magnetic field is of paramount importance in solar and heliospheric physics. Two profoundly different views of the coronal magnetic field have emerged. In quasi-steady models, the predominant source of open magnetic field is in coronal holes. In contrast, in the interchange model, the open magnetic flux is conserved, and the coronal magnetic field can only respond to the photospheric evolution via interchange reconnection. In this view, the open magnetic flux diffuses through the closed, streamer belt fields, and substantial open flux is present in the streamer belt during solar minimum. However, Antiochos and coworkers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet—it will connect via narrow corridors to the polar coronal hole of the same polarity. This contradicts the requirements of the interchange model. We have performed an MHD simulation of the solar corona up to 20 R sun to test both the interchange model and the Antiochos conjecture. We use a synoptic map for Carrington rotation 1913 as the boundary condition for the model, with two small bipoles introduced into the region where a positive polarity extended coronal hole forms. We introduce flows at the photospheric boundary surface to see if open flux associated with the bipoles can be moved into the closed-field region. Interchange reconnection does occur in response to these motions. However, we find that the open magnetic flux cannot be simply injected into closed-field regions—the flux eventually closes down and disconnected flux is created. Flux either opens or closes, as required, to maintain topologically distinct open- and closed-field regions, with no indiscriminate mixing of the two. The early evolution conforms to the Antiochos conjecture in that a narrow corridor of open flux connects the portion of the coronal hole that is nearly detached by one of the bipoles. In the later evolution, a detached coronal hole forms, in apparent violation of the Antiochos conjecture. Further investigation reveals that this detached coronal hole is actually linked to the extended coronal hole by a separatrix footprint on the photosphere of zero width. Therefore, the essential idea of the conjecture is preserved, if we modify it to state that coronal holes in the same polarity region are always linked, either by finite width corridors or separatrix footprints. The implications of these results for interchange reconnection and the sources of the slow solar wind are briefly discussed.

The Return of Magnetic Flux to the Inner Saturnian Magnetosphere

NASA Astrophysics Data System (ADS)

Lai, Hairong; Russell, Christopher T.; Jia, Yingdong; Masters, Adam; Dougherty, Michele K.

2017-04-01

The addition of plasma to the rotating inner Saturnian magnetosphere drives the circulation of the magnetic flux. The magnetic flux is loaded with cold plasma originating from Enceladus and its plasma torus. It then convects outward to the tail region, is emptied of plasma during reconnection events, and returns buoyantly to the inner magnetosphere. Returning flux tubes carry hot and tenuous plasma that serves as a marker of this type of flux tube. The plasma inside the tubes drifts at different rates depending on energy in the curved and inhomogeneous magnetosphere when the tubes convect inward. This energy dispersion can be used to track the flux tube. With data from MAG and CAPS, we model the energy dispersion of the electrons to determine the age and the point of return of the 'empty' flux tubes. The results show that even the 'fresh' flux tubes are several hours old when seen and they start to return at 19 Saturn radii, near Titan's orbit. This supports the hypothesis that returning flux tubes generated by reconnection in the far-tail region are injected directly into the inner magnetosphere.

Two-dimensional magnetohydrodynamic model of emerging magnetic flux in the solar atmosphere

NASA Technical Reports Server (NTRS)

Shibata, K.; Tajima, T.; Steinolfson, R. S.; Matsumoto, R.

1989-01-01

The nonlinear undular mode of the magnetic buoyancy instability in an isolated horizontal magnetic flux embedded in a two-temperature layered atmosphere (solar corona-chromosphere/photosphere) is investigated using a two-dimensional magnetohydrodynamic code. The results show that the flux sheet with beta of about 1 is initially located at the bottom of the photosphere, and that the gas slides down the expanding loop as the instability develops, with the evacuated loop rising as a result of enhanced magnetic buoyancy. The expansion of the magnetic loop in the nonlinear regime displays self-similar behavior. The rise velocity of the magnetic loop in the high chromosphere (10-15 km/s) and the velocity of downflow noted along the loop (30-50 km/s) are consistent with observed values for arch filament systems.

Magnetic flux rope versus the spheromak as models for interplanetary magnetic clouds

NASA Technical Reports Server (NTRS)

Farrugia, C. J.; Osherovich, V. A.; Burlaga, L. F.

1995-01-01

Magnetic clouds form a subset of interplanetary ejecta with well-defined magnetic and thermodynamic properties. Observationally, it is well established that magnetic clouds expand as they propagate antisunward. The aim of this paper is to compare and contrast two models which have been proposed for the global magnetic field line topology of magnetic clouds: a magnetic flux tube geometry, on the one hand, and a spheromak geometry (including possible higher multiples), on the other. Traditionally, the magnetic structure of magnetic clouds has been modeled by force-free configurations. In a first step, we therefore analyze the ability of static force-free models to account for the asymmetries observed in the magnetic field profiles of magnetic clouds. For a cylindrical flux tube the magnetic field remains symmetric about closest approach to the magnetic axis on all spacecraft orbits intersecting it, whereas in a spheromak geometry one can have asymmetries in the magnetic field signatures along some spacecraft trajectories. The duration of typical magnetic cloud encounters at 1 AU (1 to 2 days) is comparable to their travel time from the Sun to 1 AU and thus magnetic clouds should be treated as strongly nonstationary objects. In a second step, therefore, we abandon the static approach and model magnetic clouds as self-similarly evolving MHD configurations. In our theory, the interaction of the expanding magnetic cloud with the ambient plasma is taken into account by a drag force proportional to the density and the velocity of expansion. Solving rigorously the full set of MHD equations, we demonstrate that the asymmetry in the magnetic signature may arise solely as a result of expansion. Using asymptotic solutions of the MHD equations, we least squares fit both theoretical models to interplanetary data. We find that while the central part of the magnetic cloud is adequately described by both models, the 'edges' of the cloud data are modeled better by the magnetic flux tube. Further comparisons of the two models necessarily involve thermodynamic properties, since real magnetic configurations are never exactly force-free and gas pressure plays an essential role. We consider a polytropic gas. Our theoretical analysis shows that the self-similar expansion of a magnetic flux tube requires the polytropic index gamma to be less than unity. For the spheromak, however, self-similar, radially expanding solutions are known only for gamma equal to 4/3. This difference, therefore, yields a good way of distinguishing between the two geometries. It has been shown recently that the polytropic relationship is applicable to magnetic clouds and that the corresponding polytropic index is approximately 0.5. This observational result is consistent with the self-similar model of the magnetic flux rope but is in conflict with the self-similar spheromak model.

MODELING THE RISE OF FIBRIL MAGNETIC FIELDS IN FULLY CONVECTIVE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weber, Maria A.; Browning, Matthew K., E-mail: mweber@astro.ex.ac.uk

Many fully convective stars exhibit a wide variety of surface magnetism, including starspots and chromospheric activity. The manner by which bundles of magnetic field traverse portions of the convection zone to emerge at the stellar surface is not especially well understood. In the solar context, some insight into this process has been gleaned by regarding the magnetism as consisting partly of idealized thin flux tubes (TFTs). Here we present the results of a large set of TFT simulations in a rotating spherical domain of convective flows representative of a 0.3 M {sub ⊙} main-sequence star. This is the first studymore » to investigate how individual flux tubes in such a star might rise under the combined influence of buoyancy, convection, and differential rotation. A time-dependent hydrodynamic convective flow field, taken from separate 3D simulations calculated with the anelastic equations, impacts the flux tube as it rises. Convective motions modulate the shape of the initially buoyant flux ring, promoting localized rising loops. Flux tubes in fully convective stars have a tendency to rise nearly parallel to the rotation axis. However, the presence of strong differential rotation allows some initially low-latitude flux tubes of moderate strength to develop rising loops that emerge in the near-equatorial region. Magnetic pumping suppresses the global rise of the flux tube most efficiently in the deeper interior and at lower latitudes. The results of these simulations aim to provide a link between dynamo-generated magnetic fields, fluid motions, and observations of starspots for fully convective stars.« less

MAGNETAR GIANT FLARES-FLUX ROPE ERUPTIONS IN MULTIPOLAR MAGNETOSPHERIC MAGNETIC FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu Cong, E-mail: cyu@ynao.ac.cn

2012-09-20

We address a primary question regarding the physical mechanism that triggers the energy release and initiates the onset of eruptions in the magnetar magnetosphere. Self-consistent stationary, axisymmetric models of the magnetosphere are constructed based on force-free magnetic field configurations that contain a helically twisted force-free flux rope. Depending on the surface magnetic field polarity, there exist two kinds of magnetic field configurations, inverse and normal. For these two kinds of configurations, variations of the flux rope equilibrium height in response to gradual surface physical processes, such as flux injections and crust motions, are carefully examined. We find that equilibrium curvesmore » contain two branches: one represents a stable equilibrium branch, and the other an unstable equilibrium branch. As a result, the evolution of the system shows a catastrophic behavior: when the magnetar surface magnetic field evolves slowly, the height of the flux rope would gradually reach a critical value beyond which stable equilibriums can no longer be maintained. Subsequently, the flux rope would lose equilibrium and the gradual quasi-static evolution of the magnetosphere will be replaced by a fast dynamical evolution. In addition to flux injections, the relative motion of active regions would give rise to the catastrophic behavior and lead to magnetic eruptions as well. We propose that a gradual process could lead to a sudden release of magnetosphere energy on a very short dynamical timescale, without being initiated by a sudden fracture in the crust of the magnetar. Some implications of our model are also discussed.« less

Coronal Flux Rope Catastrophe Associated With Internal Energy Release

NASA Astrophysics Data System (ADS)

Zhuang, Bin; Hu, Youqiu; Wang, Yuming; Zhang, Quanhao; Liu, Rui; Gou, Tingyu; Shen, Chenglong

2018-04-01

Magnetic energy during the catastrophe was predominantly studied by the previous catastrophe works since it is believed to be the main energy supplier for the solar eruptions. However, the contribution of other types of energies during the catastrophe cannot be neglected. This paper studies the catastrophe of the coronal flux rope system in the solar wind background, with emphasis on the transformation of different types of energies during the catastrophe. The coronal flux rope is characterized by its axial and poloidal magnetic fluxes and total mass. It is shown that a catastrophe can be triggered by not only an increase but also a decrease of the axial magnetic flux. Moreover, the internal energy of the rope is found to be released during the catastrophe so as to provide energy for the upward eruption of the flux rope. As far as the magnetic energy is concerned, it provides only part of the energy release, or even increases during the catastrophe, so the internal energy may act as the dominant or even the unique energy supplier during the catastrophe.

Slow twists of solar magnetic flux tubes and the polar magnetic field of the sun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, M.A.; Hollweg, J.V.

The solar wind model of Weber and Davis (1967) is generalized to compute the heliospheric magnetic field resulting from solar rotation or a steady axisymmetric twist including a geometrical expansion which is more rapid than spherical. The calculated increase in the ratio of the toroidal to poloidal field components with heliocentric radial distance r clarifies an expression derived recently by Jokipii and Kota (1989). Magnetic field components transverse to r do not in general grow to dominate the radial component at large r. The analysis also yield expressions for the Poynting flux associated with the steady twists. These results aremore » regarded as indicative of the Poynting flux associated with very low frequency Alfven waves, and it is shown how the Poynting flux and the spatial evolution of the wave amplitude differ from the usual WKB result. It is found that the low-frequency Poynting flux at the base of a coronal hole can be about 50 percent larger than the WKB flux inferred from spectral observations of coronal motions (e.g. Hassler et al., 1988).« less

Magnetic strength and corrosion of rare earth magnets.

PubMed

Ahmad, Khalid A; Drummond, James L; Graber, Thomas; BeGole, Ellen

2006-09-01

Rare earth magnets have been used in orthodontics, but their corrosion tendency in the oral cavity limits long-term clinical application. The aim of this project was to evaluate several; magnet coatings and their effects on magnetic flux density. A total of 60 neodymium-iron-boron magnets divided into 6 equal groups--polytetrafluoroethylene-coated (PTFE), parylene-coated, and noncoated--were subjected to 4 weeks of aging in saline solution, ball milling, and corrosion testing. A significant decrease in magnet flux density was recorded after applying a protective layer of parylene, whereas a slight decrease was found after applying a protective layer of PTFE. After 4 weeks of aging, the coated magnets were superior to the noncoated magnets in retaining magnetism. The corrosion-behavior test showed no significant difference between the 2 types of coated magnets, and considerable amounts of iron-leached ions were seen in all groups. Throughout the processes of coating, soaking, ball milling, and corrosion testing, PTFE was a better coating material than parylene for preserving magnet flux density. However, corrosion testing showed significant metal leaching in all groups.

A new method to determine magnetic properties of the unsaturated-magnetized rotor of a novel gyro

NASA Astrophysics Data System (ADS)

Li, Hai; Liu, Xiaowei; Dong, Changchun; Zhang, Haifeng

2016-06-01

A new method is proposed to determine magnetic properties of the unsaturated-magnetized, small and irregular shaped rotor of a novel gyro. The method is based on finite-element analysis and the measurements of the magnetic flux density distribution, determining magnetic parameters by comparing the magnetic flux intensity distribution differences between the modeling results under different parameters and the measured ones. Experiment on a N30 Grade NdFeB magnet shows that its residual magnetic flux density is 1.10±0.01 T, and coercive field strength is 801±3 kA/m, which are consistent with the given parameters of the material. The method was applied to determine the magnetic properties of the rotor of the gyro, and the magnetic properties acquired were used to predict the open-loop gyro precession frequency. The predicted precession frequency should be larger than 12.9 Hz, which is close to the experimental result 13.5 Hz. The result proves that the method is accurate in estimating the magnetic properties of the rotor of the gyro.

Public roads : a journal of highway research. Vol. 25, No. 10

DOT National Transportation Integrated Search

1949-10-01

In this issue of Public Roads appears the first portion of an important work on highway capacity and its practical applications. The second half of the report, dealing with intersections at grade, weaving sections and unsignalized cross movements, ra...

Safety, operational, and energy impacts of in-vehicle adaptive stop displays using connected vehicle technology.

DOT National Transportation Integrated Search

2015-07-01

Un-signalized intersections create multiple opportunities for missed or misunderstood information. : Stop sign-controlled intersections have also been shown to be a source of delay and emissions due : to their frequent, often inappropriate use. By us...

Improved Readout Scheme for SQUID-Based Thermometry

NASA Technical Reports Server (NTRS)

Penanen, Konstantin

2007-01-01

An improved readout scheme has been proposed for high-resolution thermometers, (HRTs) based on the use of superconducting quantum interference devices (SQUIDs) to measure temperature- dependent magnetic susceptibilities. The proposed scheme would eliminate counting ambiguities that arise in the conventional scheme, while maintaining the superior magnetic-flux sensitivity of the conventional scheme. The proposed scheme is expected to be especially beneficial for HRT-based temperature control of multiplexed SQUIDbased bolometer sensor arrays. SQUID-based HRTs have become standard for measuring and controlling temperatures in the sub-nano-Kelvin temperature range in a broad range of low-temperature scientific and engineering applications. A typical SQUIDbased HRT that utilizes the conventional scheme includes a coil wound on a core made of a material that has temperature- dependent magnetic susceptibility in the temperature range of interest. The core and the coil are placed in a DC magnetic field provided either by a permanent magnet or as magnetic flux inside a superconducting outer wall. The aforementioned coil is connected to an input coil of a SQUID. Changes in temperature lead to changes in the susceptibility of the core and to changes in the magnetic flux detected by the SQUID. The SQUID readout instrumentation is capable of measuring magnetic-flux changes that correspond to temperature changes down to a noise limit .0.1 nK/Hz1/2. When the flux exceeds a few fundamental flux units, which typically corresponds to a temperature of .100 nK, the SQUID is reset. The temperature range can be greatly expanded if the reset events are carefully tracked and counted, either by a computer running appropriate software or by a dedicated piece of hardware.

Evidence in Magnetic Clouds for Systematic Open Flux Transport on the Sun

NASA Technical Reports Server (NTRS)

Crooker, N. U.; Kahler, S. W.; Gosling, J. T.; Lepping, R. P.

2008-01-01

Most magnetic clouds encountered by spacecraft at 1 AU display a mix of unidirectional suprathermal electrons signaling open field lines and counterstreaming electrons signaling loops connected to the Sun at both ends. Assuming the open fields were originally loops that underwent interchange reconnection with open fields at the Sun, we determine the sense of connectedness of the open fields found in 72 of 97 magnetic clouds identified by the Wind spacecraft in order to obtain information on the location and sense of the reconnection and resulting flux transport at the Sun. The true polarity of the open fields in each magnetic cloud was determined from the direction of the suprathermal electron flow relative to the magnetic field direction. Results indicate that the polarity of all open fields within a given magnetic cloud is the same 89% of the time, implying that interchange reconnection at the Sun most often occurs in only one leg of a flux rope loop, thus transporting open flux in a single direction, from a coronal hole near that leg to the foot point of the opposite leg. This pattern is consistent with the view that interchange reconnection in coronal mass ejections systematically transports an amount of open flux sufficient to reverse the polarity of the heliospheric field through the course of the solar cycle. Using the same electron data, we also find that the fields encountered in magnetic clouds are only a third as likely to be locally inverted as not. While one might expect inversions to be equally as common as not in flux rope coils, consideration of the geometry of spacecraft trajectories relative to the modeled magnetic cloud axes leads us to conclude that the result is reasonable.

Asymptotic domination of cold relativistic MHD winds by kinetic energy flux

NASA Technical Reports Server (NTRS)

Begelman, Mitchell C.; Li, Zhi-Yun

1994-01-01

We study the conditions which lead to the conversion of most Poynting flux into kinetic energy flux in cold, relativistic hydromagnetic winds. It is shown that plasma acceleration along a precisely radial flow is extremely inefficient due to the near cancellation of the toroidal magnetic pressure and tension forces. However, if the flux tubes in a flow diverge even slightly faster than radially, the fast magnetosonic point moves inward from infinity to a few times the light cylinder radius. Once the flow becomes supermagnetosonic, further divergence of the flux tubes beyond the fast point can accelerate the flow via the 'magnetic nozzle' effect, thereby further converting Poynting flux to kinetic energy flux. We show that the Grad-Shafranov equation admits a generic family of kinetic energy-dominated asymptotic wind solutions with finite total magnetic flux. The Poynting flux in these solutions vanishes logarithmically with distance. The way in which the flux surfaces are nested within the flow depends only on the ratio of angular velocity to poliodal 4-velocity as a function of magnetic flux. Radial variations in flow structure can be expressed in terms of a pressure boundary condition on the outermost flux surface, provided that no external toriodal field surrounds the flow. For a special case, we show explicitly how the flux surfaces merge gradually to their asymptotes. For flows confined by an external medium of pressure decreasing to zero at infinity we show that, depending on how fast the ambient pressure declines, the final flow state could be either a collimated jet or a wind that fills the entire space. We discuss the astrophysical implications of our results for jets from active galactic nuclei and for free pulsar winds such as that believed to power the Crab Nebula.

Superconducting Effects in Optimization of Magnetic Penetration Thermometers for X-ray Microcalorimeters

NASA Technical Reports Server (NTRS)

Stevenson, Thomas R.; Balvin, M. A.; Denis, K. L.; Hsieh, W.-T.; Sadleir, J. E.; Bandler, Simon E.; Busch, Sarah E.; Merrell, W.; Kelly, Daniel P.; Nagler, Peter C.;

ASYMMETRY OF HELICITY INJECTION FLUX IN EMERGING ACTIVE REGIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian Lirong; Alexander, David

Observational and modeling results indicate that typically the leading magnetic field of bipolar active regions (ARs) is often spatially more compact, while more dispersed and fragmented in following polarity. In this paper, we address the origin of this morphological asymmetry, which is not well understood. Although it may be assumed that, in an emerging {omega}-shaped flux tube, those portions of the flux tube in which the magnetic field has a higher twist may maintain its coherence more readily, this has not been tested observationally. To assess this possibility, it is important to characterize the nature of the fragmentation and asymmetrymore » in solar ARs and this provides the motivation for this paper. We separately calculate the distribution of the helicity flux injected in the leading and following polarities of 15 emerging bipolar ARs, using the Michelson Doppler Image 96 minute line-of-sight magnetograms and a local correlation tracking technique. We find from this statistical study that the leading (compact) polarity injects several times more helicity flux than the following (fragmented) one (typically 3-10 times). This result suggests that the leading polarity of the {omega}-shaped flux tube possesses a much larger amount of twist than the following field prior to emergence. We argue that the helicity asymmetry between the leading and following magnetic field for the ARs studied here results in the observed magnetic field asymmetry of the two polarities due to an imbalance in the magnetic tension of the emerging flux tube. We suggest that the observed imbalance in the helicity distribution results from a difference in the speed of emergence between the leading and following legs of an inclined {omega}-shaped flux tube. In addition, there is also the effect of magnetic flux imbalance between the two polarities with the fragmented following polarity displaying spatial fluctuation in both the magnitude and sign of helicity measured.« less

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE.

PubMed

Möstl, C; Amerstorfer, T; Palmerio, E; Isavnin, A; Farrugia, C J; Lowder, C; Winslow, R M; Donnerer, J M; Kilpua, E K J; Boakes, P D

2018-03-01

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3-D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward-pointing magnetic fields. Here we demonstrate in a proof-of-concept way a new approach to predict the southward field B z in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three-Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun-Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9-13 July 2013. Three-Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3-D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left-handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE

NASA Astrophysics Data System (ADS)

Möstl, C.; Amerstorfer, T.; Palmerio, E.; Isavnin, A.; Farrugia, C. J.; Lowder, C.; Winslow, R. M.; Donnerer, J. M.; Kilpua, E. K. J.; Boakes, P. D.

2018-03-01

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3-D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward-pointing magnetic fields. Here we demonstrate in a proof-of-concept way a new approach to predict the southward field Bz in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three-Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun-Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9-13 July 2013. Three-Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3-D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left-handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.

Magnetic Turbulence, Fast Magnetic Field line Diffusion and Small Magnetic Structures in the Solar Wind

NASA Astrophysics Data System (ADS)

Zimbardo, G.; Pommois, P.; Veltri, P.

2003-09-01

The influence of magnetic turbulence on magnetic field line diffusion has been known since the early days of space and plasma physics. However, the importance of ``stochastic diffusion'' for energetic particles has been challenged on the basis of the fact that sharp gradients of either energetic particles or ion composition are often observed in the solar wind. Here we show that fast transverse field line and particle diffusion can coexist with small magnetic structures, sharp gradients, and with long lived magnetic flux tubes. We show, by means of a numerical realization of three dimensional magnetic turbulence and by use of the concepts of deterministic chaos and turbulent transport, that turbulent diffusion is different from Gaussian diffusion, and that transport can be inhomogeneous even if turbulence homogeneously fills the heliosphere. Several diagnostics of field line transport and flux tube evolution are shown, and the size of small magnetic structures in the solar wind, like gradient scales and flux tube thickness, are estimated and compared to the observations.

Multi-Site λ-dynamics for simulated Structure-Activity Relationship studies

PubMed Central

Knight, Jennifer L.; Brooks, Charles L.

2011-01-01

Multi-Site λ-dynamics (MSλD) is a new free energy simulation method that is based on λ-dynamics. It has been developed to enable multiple substituents at multiple sites on a common ligand core to be modeled simultaneously and their free energies assessed. The efficacy of MSλD for estimating relative hydration free energies and relative binding affinties is demonstrated using three test systems. Model compounds representing multiple identical benzene, dihydroxybenzene and dimethoxybenzene molecules show total combined MSλD trajectory lengths of ~1.5 ns are sufficient to reliably achieve relative hydration free energy estimates within 0.2 kcal/mol and are less sensitive to the number of trajectories that are used to generate these estimates for hybrid ligands that contain up to ten substituents modeled at a single site or five substituents modeled at each of two sites. Relative hydration free energies among six benzene derivatives calculated from MSλD simulations are in very good agreement with those from alchemical free energy simulations (with average unsigned differences of 0.23 kcal/mol and R2=0.991) and experiment (with average unsigned errors of 1.8 kcal/mol and R2=0.959). Estimates of the relative binding affinities among 14 inhibitors of HIV-1 reverse transcriptase obtained from MSλD simulations are in reasonable agreement with those from traditional free energy simulations and experiment (average unsigned errors of 0.9 kcal/mol and R2=0.402). For the same level of accuracy and precision MSλD simulations are achieved ~20–50 times faster than traditional free energy simulations and thus with reliable force field parameters can be used effectively to screen tens to hundreds of compounds in structure-based drug design applications. PMID:22125476

Signed weighted gene co-expression network analysis of transcriptional regulation in murine embryonic stem cells

PubMed Central

Mason, Mike J; Fan, Guoping; Plath, Kathrin; Zhou, Qing; Horvath, Steve

2009-01-01

Background Recent work has revealed that a core group of transcription factors (TFs) regulates the key characteristics of embryonic stem (ES) cells: pluripotency and self-renewal. Current efforts focus on identifying genes that play important roles in maintaining pluripotency and self-renewal in ES cells and aim to understand the interactions among these genes. To that end, we investigated the use of unsigned and signed network analysis to identify pluripotency and differentiation related genes. Results We show that signed networks provide a better systems level understanding of the regulatory mechanisms of ES cells than unsigned networks, using two independent murine ES cell expression data sets. Specifically, using signed weighted gene co-expression network analysis (WGCNA), we found a pluripotency module and a differentiation module, which are not identified in unsigned networks. We confirmed the importance of these modules by incorporating genome-wide TF binding data for key ES cell regulators. Interestingly, we find that the pluripotency module is enriched with genes related to DNA damage repair and mitochondrial function in addition to transcriptional regulation. Using a connectivity measure of module membership, we not only identify known regulators of ES cells but also show that Mrpl15, Msh6, Nrf1, Nup133, Ppif, Rbpj, Sh3gl2, and Zfp39, among other genes, have important roles in maintaining ES cell pluripotency and self-renewal. We also report highly significant relationships between module membership and epigenetic modifications (histone modifications and promoter CpG methylation status), which are known to play a role in controlling gene expression during ES cell self-renewal and differentiation. Conclusion Our systems biologic re-analysis of gene expression, transcription factor binding, epigenetic and gene ontology data provides a novel integrative view of ES cell biology. PMID:19619308

Magnetar Giant Flares in Multipolar Magnetic Fields. III. Multipolar Magnetic Field Structure Variations

NASA Astrophysics Data System (ADS)

Yao, Guang-Rui; Huang, Lei; Yu, Cong; Shen, Zhi-Qiang

2018-02-01

We have analyzed the multipolar magnetic field structure variation at neutron star surface by means of the catastrophic eruption model and find that the variation of the geometry of multipolar fields on the magnetar surface could result in the catastrophic rearrangement of the magnetosphere, which provides certain physical mechanism for the outburst of giant flares. The magnetospheric model we adopted consists of two assumptions: (1) a helically twisted flux rope is suspended in an ideal force-free magnetosphere around the magnetar, and (2) a current sheet emerges during the flux rope evolution. Magnetic energy accumulates during the flux rope’s gradual evolution along with the variation of magnetar surface magnetic structure before the eruption. The two typical behaviors, either state transition or catastrophic escape, would take place once the flux rope loses equilibrium; thus, tremendous accumulated energy is radiated. We have investigated the equilibrium state of the flux rope and the energy release affected by different multipolar structures and find structures that could trigger violent eruption and provide the radiation approximately 0.5% of the total magnetic energy during the giant flare outburst. Our results provide certain multipolar structures of the neutron star’s magnetic field with an energy release percentage 0.42% in the state transition and 0.51% in the catastrophic escape case, which are sufficient for the previously reported energy release from SGR 1806–20 giant flares.

On the Motion of the Field of a Permanent Magnet

ERIC Educational Resources Information Center

Leus, Vladimir; Taylor, Stephen

2011-01-01

A description is given of a series of recent experiments using a rotating magnetic circuit comprising a permanent magnet ring and yoke, and a stationary conductor in the air gap between the ring and yoke. The EMF induced in this case cannot be described by a simple application of Faraday's flux law. This is because the magnetic flux in the air gap…

Shipboard Elevator Magnetic Sensor Development. Phase I, Laboratory Investigations.

DTIC Science & Technology

1981-08-19

greater detail. The principles studied were those of the flux-meter and the flux-gate magnetometer . Of these two, the flux-gate magnetometer principle was...Abstract (Continued) Flux-gate magnetometers continuously sense the component of a stationary or slowly varying magnetic field along a chosen axis. The...distance of the sensor from the target’s line of travel, while precisely indicating displacements along the line. The modes of detection include level

Magnetic flux relaxation in YBa2Cu3)(7-x) thin film: Thermal or athermal

NASA Technical Reports Server (NTRS)

Vitta, Satish; Stan, M. A.; Warner, J. D.; Alterovitz, S. A.

1991-01-01

The magnetic flux relaxation behavior of YBa2Cu3O(7-x) thin film on LaAlO3 for H is parallel to c was studied in the range 4.2 - 40 K and 0.2 - 1.0 T. Both the normalized flux relaxation rate S and the net flux pinning energy U increase continuously from 1.3 x 10(exp -2) to 3.0 x 10(exp -2) and from 70 to 240 meV respectively, as the temperature T increases from 10 to 40 K. This behavior is consistent with the thermally activated flux motion model. At low temperatures, however, S is found to decrease much more slowly as compared with kT, in contradiction to the thermal activation model. This behavior is discussed in terms of the athermal quantum tunneling of flux lines. The magnetic field dependence of U, however, is not completely understood.

Magnetic flux relaxation in YBa2Cu3O(7-x) thin film: Thermal or athermal

NASA Technical Reports Server (NTRS)

Vitta, Satish; Stan, M. A.; Warner, Joseph D.; Alterovitz, Samuel A.

1992-01-01

The magnetic flux relaxation behavior of YBa2Cu3O(7-x) thin film on LaAlO3 for H parallel c was studied in the range of 4.2-40 k and 0.2-1.0 T. Both the normalized flux relaxation rate (S) and the net flux pinning energy (U) increase continuously from 1.3 x 10 exp -2 to 3.0 x 10 exp -2 and from 70-240 meV respectively, as the temperature (T) increases from 10 to 40 K. This behavior is consistent with the thermally activated flux motion model. At low temperatures, however, S is found to decrease much more slowly as compared with kT, in contradiction to the thermal activation model. This behavior is discussed in terms of the athermal quantum tunneling of flux lines. The magnetic field dependence of U, however, is not completely understood.

Interplanetary Magnetic Flux Ropes as Agents Connecting Solar Eruptions and Geomagnetic Activities

NASA Astrophysics Data System (ADS)

Marubashi, K.; Cho, K.-S.; Ishibashi, H.

2017-12-01

We investigate the solar wind structure for 11 cases that were selected for the campaign study promoted by the International Study of Earth-affecting Solar Transients (ISEST) MiniMax24 Working Group 4. We can identify clear flux rope signatures in nine cases. The geometries of the nine interplanetary magnetic flux ropes (IFRs) are examined with a model-fitting analysis with cylindrical and toroidal force-free flux rope models. For seven cases in which magnetic fields in the solar source regions were observed, we compare the IFR geometries with magnetic structures in their solar source regions. As a result, we can confirm the coincidence between the IFR orientation and the orientation of the magnetic polarity inversion line (PIL) for six cases, as well as the so-called helicity rule as regards the handedness of the magnetic chirality of the IFR, depending on which hemisphere of the Sun the IFR originated from, the northern or southern hemisphere; namely, the IFR has right-handed (left-handed) magnetic chirality when it is formed in the southern (northern) hemisphere of the Sun. The relationship between the orientation of IFRs and PILs can be taken as evidence that the flux rope structure created in the corona is in most cases carried through interplanetary space with its orientation maintained. In order to predict magnetic field variations on Earth from observations of solar eruptions, further studies are needed about the propagation of IFRs because magnetic fields observed at Earth significantly change depending on which part of the IFR hits the Earth.

FLUX CANCELLATION AND THE EVOLUTION OF THE ERUPTIVE FILAMENT OF 2011 JUNE 7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yardley, S. L.; Green, L. M.; Williams, D. R.

We investigate whether flux cancellation is responsible for the formation of a very massive filament resulting in the spectacular eruption on 2011 June 7. We analyze and quantify the amount of flux cancellation that occurs in NOAA AR 11226 and its two neighboring active regions (ARs 11227 and 11233) using line-of-sight magnetograms from the Heliospheric Magnetic Imager. During a 3.6 day period building up to the eruption of the filament, 1.7 × 10{sup 21} Mx, 21% of AR 11226's maximum magnetic flux, was canceled along the polarity inversion line (PIL) where the filament formed. If the flux cancellation continued atmore » the same rate up until the eruption then up to 2.8 × 10{sup 21} Mx (34% of the AR flux) may have been built into the magnetic configuration that contains the filament plasma. The large flux cancellation rate is due to an unusual motion of the positive-polarity sunspot, which splits, with the largest section moving rapidly toward the PIL. This motion compresses the negative polarity and leads to the formation of an orphan penumbra where one end of the filament is rooted. Dense plasma threads above the orphan penumbra build into the filament, extending its length, and presumably injecting material into it. We conclude that the exceptionally strong flux cancellation in AR 11226 played a significant role in the formation of its unusually massive filament. In addition, the presence and coherent evolution of bald patches in the vector magnetic field along the PIL suggest that the magnetic field configuration supporting the filament material is that of a flux rope.« less

Magnetic Flux Cancellation as the Origin of Solar Quiet-region Pre-jet Minifilaments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L., E-mail: navdeep.k.panesar@nasa.gov

We investigate the origin of 10 solar quiet-region pre-jet minifilaments , using EUV images from the Solar Dynamics Observatory ( SDO )/Atmospheric Imaging Assembly (AIA) and magnetograms from the SDO Helioseismic and Magnetic Imager (HMI). We recently found that quiet-region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancellation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancellation between minority-polarity and majority-polarity flux patches. In each of 10 pre-jet regions, we find that opposite-polarity patches of magneticmore » flux converge and cancel, with a flux reduction of 10%–40% from before to after the minifilament appears. For our 10 events, the minifilaments exist for periods ranging from 1.5 hr to 2 days before erupting to make a jet. Apparently, the flux cancellation builds a highly sheared field that runs above and traces the neutral line, and the cool transition region plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancellation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus, our observations strongly support that quiet-region magnetic flux cancellation results in both the formation of the pre-jet minifilament and its jet-driving eruption.« less

Evolution of vector magnetic fields and the August 27 1990 X-3 flare

NASA Technical Reports Server (NTRS)

Wang, Haimin

1992-01-01

Vector magnetic fields in an active region of the sun are studied by means of continuous observations of magnetic-field evolution emphasizing magnetic shear build-up. The vector magnetograms are shown to measure magnetic fields correctly based on concurrent observations and a comparison of the transverse field with the H alpha fibril structure. The morphology and velocity pattern are examined, and these data and the shear build-up suggest that the active region's two major footprints are separated by a region with flows, new flux emergence, and several neutral lines. The magnetic shear appears to be caused by the collision and shear motion of two poles of opposite polarities. The transverse field is shown to turn from potential to sheared during the process of flux cancellation, and this effect can be incorporated into existing models of magnetic flux cancellation.

Magnetic field distribution in superconducting composites as revealed by ESR-probe and magnetization

NASA Astrophysics Data System (ADS)

Davidov, D.; Bontemps, N.; Golosovsky, M.; Waysand, G.

1998-03-01

The distribution of a static magnetic field in superconductor-insulator composites consisting of BSCCO (YBCO) powder in paraffin wax is studied by ESR bulk probing and magnetization. The average field and field variance in the non-superconducting host are measured as function of temperature and volume fraction of superconductor. We develop a model of the field distribution in dilute magnetic and superconducting composites that relates the field inhomogeneity to magnetization and particle shape. We find that this model satisfactorily describes field distribution in our superconducting composites in the regime of strong flux pinning, i.e. below irreversibility line. We find deviations from the model above the irreversibility line and attribute this to flux motion. We show that the field distribution in superconducting composites is determined not only by magnetization and particle shape, but is strongly affected by the flux profile within the superconducting particles.

Shock wave propagation in a magnetic flux tube

NASA Astrophysics Data System (ADS)

Ferriz-Mas, A.; Moreno-Insertis, F.

1992-12-01

The propagation of a shock wave in a magnetic flux tube is studied within the framework of the Brinkley-Kirkwood theory adapted to a radiating gas. Simplified thermodynamic paths along which the compressed plasma returns to its initial state are considered. It is assumed that the undisturbed medium is uniform and that the flux tube is optically thin. The shock waves investigated, which are described with the aid of the thin flux-tube approximation, are essentially slow magnetohydrodynamic shocks modified by the constraint of lateral pressure balance between the flux tube and the surrounding field-free fluid; the confining external pressure must be balanced by the internal gas plus magnetic pressures. Exact analytical solutions giving the evolution of the shock wave are obtained for the case of weak shocks.

A Novel Transverse Flux Machine for Vehicle Traction Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Zhao; Ahmed, Adeeb; Husain, Iqbal

2015-10-05

A novel transverse flux machine topology for electric vehicle traction application using ferrite magnets is presented in this paper. The proposed transverse flux topology utilizes novel magnet arrangements in the rotor that are similar to Halbach-array to boost flux linkage; on the stator side, cores are alternately arranged around a pair of ring windings in each phase to make use of the entire rotor flux that eliminates end windings. Analytical design considerations and finite element methods are used for an optimized design of a scooter in-wheel motor. Simulation results from Finite Element Analysis (FEA) show the motor achieved comparable torquemore » density to conventional rare-earth permanent magnet machines. This machine is a viable candidate for direct drive applications with low cost and high torque density.« less

Plasma dynamics on current-carrying magnetic flux tubes. II - Low potential simulation

NASA Technical Reports Server (NTRS)

Swift, Daniel W.

1992-01-01

The evolution of plasma in a current-carrying magnetic flux tube of variable cross section is investigated using a one-dimensional numerical simulation. The flux tube is narrow at the two ends and broad in the middle. The middle part of the flux tube is loaded with a hot, magnetically trapped population, and the two ends have a more dense, gravitationally bound population. A potential difference larger than the gravitational potential but less than the energy of the hot population is applied across the domain. The general result is that the potential change becomes distributed along the anode half of the domain, with negligible potential change on the cathode half. The potential is supported by the mirror force of magnetically trapped particles. The simulations show a steady depletion of plasma on the anode side of the flux tube. The current steadily decreases on a time scale of an ion transit time. The results may provide an explanation for the observed plasma depletions on auroral field lines carrying upward currents.

AN ESTIMATE OF THE DETECTABILITY OF RISING FLUX TUBES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Birch, A. C.; Braun, D. C.; Fan, Y., E-mail: aaronb@cora.nwra.co

The physics of the formation of magnetic active regions (ARs) is one of the most important problems in solar physics. One main class of theories suggests that ARs are the result of magnetic flux that rises from the tachocline. Time-distance helioseismology, which is based on measurements of wave propagation, promises to allow the study of the subsurface behavior of this magnetic flux. Here, we use a model for a buoyant magnetic flux concentration together with the ray approximation to show that the dominant effect on the wave propagation is expected to be from the roughly 100 m s{sup -1} retrogrademore » flow associated with the rising flux. Using a B-spline-based method for carrying out inversions of wave travel times for flows in spherical geometry, we show that at 3 days before emergence the detection of this retrograde flow at a depth of 30 Mm should be possible with a signal-to-noise level of about 8 with a sample of 150 emerging ARs.« less

The local time dependence of the anisotropic solar cosmic ray flux.

PubMed

Smart, D F; Shea, M A

2003-01-01

The distribution of the solar cosmic radiation flux over the earth is not uniform, but the result of complex phenomena involving the interplanetary magnetic field, the geomagnetic field and latitude and longitude of locations on the earth. The latitude effect relates to the geomagnetic shield; the longitude effect relates to local time. For anisotropic solar cosmic ray events the maximum particle flux is always along the interplanetary magnetic field direction, sometimes called the Archimedean spiral path from the sun to the earth. During anisotropic solar cosmic ray event, the locations on the earth viewing "sunward" into the interplanetary magnetic field direction will observe the largest flux (when adjustments are made for the magnetic latitude effect). To relate this phenomena to aircraft routes, for anisotropic solar cosmic ray events that occur during "normal quiescent" conditions, the maximum solar cosmic ray flux (and corresponding solar particle radiation dose) will be observed in the dawn quadrant, ideally at about 06 hours local time. Published by Elsevier Ltd on behalf of COSPAR.

Efficient expulsion of magnetic flux in superconducting radiofrequency cavities for high Q 0 applications

DOE PAGES

Posen, S.; Checchin, M.; Crawford, A. C.; ...

2016-06-03

Even when cooled through its transition temperature in the presence of an external magnetic field, a superconductor can expel nearly all external magnetic flux. This Letter presents an experimental study to identify the parameters that most strongly influence flux trapping in high purity niobium during cooldown. This is critical to the operation of superconducting radiofrequency cavities, in which trapped flux degrades the quality factor and therefore cryogenic efficiency. Flux expulsion was measured on a large survey of 1.3 GHz cavities prepared in various ways. It is shown that both spatial thermal gradient and high temperature treatment are critical to expellingmore » external magnetic fields, while surface treatment has minimal effect. For the first time, it is shown that a cavity can be converted from poor expulsion behavior to strong expulsion behavior after furnace treatment, resulting in a substantial improvement in quality factor. In conclusion, future plans are described to build on this result in order to optimize treatment for future cavities.« less

Eddy current loss analysis of open-slot fault-tolerant permanent-magnet machines based on conformal mapping method

NASA Astrophysics Data System (ADS)

Ji, Jinghua; Luo, Jianhua; Lei, Qian; Bian, Fangfang

2017-05-01

This paper proposed an analytical method, based on conformal mapping (CM) method, for the accurate evaluation of magnetic field and eddy current (EC) loss in fault-tolerant permanent-magnet (FTPM) machines. The aim of modulation function, applied in CM method, is to change the open-slot structure into fully closed-slot structure, whose air-gap flux density is easy to calculate analytically. Therefore, with the help of Matlab Schwarz-Christoffel (SC) Toolbox, both the magnetic flux density and EC density of FTPM machine are obtained accurately. Finally, time-stepped transient finite-element method (FEM) is used to verify the theoretical analysis, showing that the proposed method is able to predict the magnetic flux density and EC loss precisely.

Flux flow induced microwave absorption in high temperature superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N

NASA Astrophysics Data System (ADS)

Owens, F. J.

1990-12-01

Direct measurements of microwave absorption without use of rf H field modulation in granular composites of the 115 K superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N as a function of magnetic field above 0.1 T reveal a continuing increase of absorption of microwave energy increasing magnetic field. The temperature and magnetic field dependence of the absorption are very different from the low magnetic field (<0.01 T) absorption arising from weak links in the material. The magnetic field and temperature dependence are consistent with the behavior of thermally activated flux flow resistance suggesting the absorption is due to flux creep.

Large-Scale Coronal Heating, Clustering of Coronal Bright Points, and Concentration of Magnetic Flux

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

1998-01-01

By combining quiet-region Fe XII coronal images from SOHO/EIT with magnetograms from NSO/Kitt Peak and from SOHO/MDI, we show that on scales larger than a supergranule the population of network coronal bright points and the magnetic flux content of the network are both markedly greater under the bright half of the quiet corona than under the dim half. These results (1) support the view that the heating of the entire corona in quiet regions and coronal holes is driven by fine-scale magnetic activity (microflares, explosive events, spicules) seated low in the magnetic network, and (2) suggest that this large-scale modulation of the magnetic flux and coronal heating is a signature of giant convection cells.

Observation of Persistent Currents in Finely Dispersed Pyrolytic Graphite

NASA Astrophysics Data System (ADS)

Saad, M.; Gilmutdinov, I. F.; Kiiamov, A. G.; Tayurskii, D. A.; Nikitin, S. I.; Yusupov, R. V.

2018-01-01

The trapped magnetic flux in the finely ground pyrolytic graphite sample annealed at 670 K in air has been observed. Flux trapping occurs on cooling of the sample from room temperature to 10 K in a magnetic field of 1 T. The magnitude and sign of the induced trapped moment remain unchanged when the applied magnetic field is varied within ±1 T at T K. The trapped magnetic flux is manifested in the displacement of the magnetization curve relative to that of the sample cooled in zero field. Displacement magnitude gradually decreases with the temperature increase up to 350 K, not reaching zero. The set of experimental observations probably reflects the presence in the sample of a granular high-temperature superconducting phase.

Squeezing of particle distributions by expanding magnetic turbulence and space weather variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruffolo, D.; Seripienlert, A.; Tooprakai, P.

Among the space weather effects due to gradual solar storms, greatly enhanced high-energy ion fluxes contribute to radiation damage to satellites, spacecraft, and astronauts and dominate the hazards to air travelers, which motivates examination of the transport of high-energy solar ions to Earth's orbit. Ions of low kinetic energy (up to ∼2 MeV nucleon{sup –1}) from impulsive solar events exhibit abrupt changes due to filamentation of the magnetic connection from the Sun, indicating that anisotropic, field-aligned magnetic flux tubelike structures persist to Earth's orbit. By employing a corresponding spherical two-component model of Alfvénic (slab) and two-dimensional magnetic fluctuations to tracemore » simulated trajectories in the solar wind, we show that the distribution of high-energy (E ≥ 1 GeV) protons from gradual solar events is squeezed toward magnetic flux structures with a specific polarity because of the conical shape of the flux structures. Conical flux structures and the squeezing of energetic particle distributions should occur in any astrophysical wind or jet with expanding, magnetized, turbulent plasma. This transport phenomenon contributes to event-to-event variability in ground level enhancements of GeV-range ions from solar storms, presenting a fundamental uncertainty in space weather prediction.« less

The spontaneous concentration of magnetic field in the photosphere of the sun

NASA Technical Reports Server (NTRS)

Parker, E. N.

1981-01-01

The basic physics of magnetic flux tubes in the solar photosphere is reviewed, with areas still open to conjecture pointed out. The question of the concentration of individual small flux tubes to levels of 1-2 kilogauss, when the average solar surface magnetic field is on the order of 10 gauss, by processes of twisting and the formation of flux ropes made up of tubes wound around each other is considered together with the effects of turbulence on the flux tube. Mechanisms for tube compression by the evacuation of the gas contained within a flux tube are then examined, and the possibility of field concentration through the cooling of the gas within the tube in a superadiabatic process is suggested. Attention is then given to possible mechanisms serving to maintain the concentration of flux tubes far below the surface of the sun which gives rise to sunspots and pores as the flux tree emerges through the surface.

Analytical Modeling of a Novel Transverse Flux Machine for Direct Drive Wind Turbine Applications: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, IIftekhar; Husain, Tausif; Uddin, Md Wasi

2015-08-24

This paper presents a nonlinear analytical model of a novel double-sided flux concentrating Transverse Flux Machine (TFM) based on the Magnetic Equivalent Circuit (MEC) model. The analytical model uses a series-parallel combination of flux tubes to predict the flux paths through different parts of the machine including air gaps, permanent magnets, stator, and rotor. The two-dimensional MEC model approximates the complex three-dimensional flux paths of the TFM and includes the effects of magnetic saturation. The model is capable of adapting to any geometry that makes it a good alternative for evaluating prospective designs of TFM compared to finite element solversmore » that are numerically intensive and require more computation time. A single-phase, 1-kW, 400-rpm machine is analytically modeled, and its resulting flux distribution, no-load EMF, and torque are verified with finite element analysis. The results are found to be in agreement, with less than 5% error, while reducing the computation time by 25 times.« less

Analytical Modeling of a Novel Transverse Flux Machine for Direct Drive Wind Turbine Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, IIftekhar; Husain, Tausif; Uddin, Md Wasi

2015-09-02

This paper presents a nonlinear analytical model of a novel double sided flux concentrating Transverse Flux Machine (TFM) based on the Magnetic Equivalent Circuit (MEC) model. The analytical model uses a series-parallel combination of flux tubes to predict the flux paths through different parts of the machine including air gaps, permanent magnets (PM), stator, and rotor. The two-dimensional MEC model approximates the complex three-dimensional flux paths of the TFM and includes the effects of magnetic saturation. The model is capable of adapting to any geometry which makes it a good alternative for evaluating prospective designs of TFM as compared tomore » finite element solvers which are numerically intensive and require more computation time. A single phase, 1 kW, 400 rpm machine is analytically modeled and its resulting flux distribution, no-load EMF and torque, verified with Finite Element Analysis (FEA). The results are found to be in agreement with less than 5% error, while reducing the computation time by 25 times.« less

Three-dimensional modeling of plasma edge transport and divertor fluxes during application of resonant magnetic perturbations on ITER

NASA Astrophysics Data System (ADS)

Schmitz, O.; Becoulet, M.; Cahyna, P.; Evans, T. E.; Feng, Y.; Frerichs, H.; Loarte, A.; Pitts, R. A.; Reiser, D.; Fenstermacher, M. E.; Harting, D.; Kirschner, A.; Kukushkin, A.; Lunt, T.; Saibene, G.; Reiter, D.; Samm, U.; Wiesen, S.

2016-06-01

Results from three-dimensional modeling of plasma edge transport and plasma-wall interactions during application of resonant magnetic perturbation (RMP) fields for control of edge-localized modes in the ITER standard 15 MA Q  =  10 H-mode are presented. The full 3D plasma fluid and kinetic neutral transport code EMC3-EIRENE is used for the modeling. Four characteristic perturbed magnetic topologies are considered and discussed with reference to the axisymmetric case without RMP fields. Two perturbation field amplitudes at full and half of the ITER ELM control coil current capability using the vacuum approximation are compared to a case including a strongly screening plasma response. In addition, a vacuum field case at high q 95  =  4.2 featuring increased magnetic shear has been modeled. Formation of a three-dimensional plasma boundary is seen for all four perturbed magnetic topologies. The resonant field amplitudes and the effective radial magnetic field at the separatrix define the shape and extension of the 3D plasma boundary. Opening of the magnetic field lines from inside the separatrix establishes scrape-off layer-like channels of direct parallel particle and heat flux towards the divertor yielding a reduction of the main plasma thermal and particle confinement. This impact on confinement is most accentuated at full RMP current and is strongly reduced when screened RMP fields are considered, as well as for the reduced coil current cases. The divertor fluxes are redirected into a three-dimensional pattern of helical magnetic footprints on the divertor target tiles. At maximum perturbation strength, these fingers stretch out as far as 60 cm across the divertor targets, yielding heat flux spreading and the reduction of peak heat fluxes by 30%. However, at the same time substantial and highly localized heat fluxes reach divertor areas well outside of the axisymmetric heat flux decay profile. Reduced RMP amplitudes due to screening or reduced RMP coil current yield a reduction of the width of the divertor flux spreading to about 20-25 cm and cause increased peak heat fluxes back to values similar to those in the axisymmetric case. The dependencies of these features on the divertor recycling regime and the perpendicular transport assumptions, as well as toroidal averaged effects mimicking rotation of the RMP field, are discussed in the paper.

Structure of sunspot penumbrae - Fallen magnetic flux tubes

NASA Technical Reports Server (NTRS)

Wentzel, Donat G.

1992-01-01

A model is presented of a sunspot penumbra involving magnetic flux tubes that have fallen into the photosphere and float there. An upwelling at the inner end of a fallen tube continuously provides additional gas. This gas flows along and lengthens the tube and is observable as the Evershed flow. Fallen flux tubes may appear as bright streaks near the upwelling, but they become dark filaments further out. The model is corroborated by recent optical high-resolution magnetic data regarding the penumbral filaments, by the 12-micron magnetic measurements relevant to the height of the temperature minimum, and by photographs of the umbra/penumbra boundary.

Regularized Biot–Savart Laws for Modeling Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Titov, Viacheslav S.; Downs, Cooper; Mikić, Zoran; Török, Tibor; Linker, Jon A.; Caplan, Ronald M.

2018-01-01

Many existing models assume that magnetic flux ropes play a key role in solar flares and coronal mass ejections (CMEs). It is therefore important to develop efficient methods for constructing flux-rope configurations constrained by observed magnetic data and the morphology of the pre-eruptive source region. For this purpose, we have derived and implemented a compact analytical form that represents the magnetic field of a thin flux rope with an axis of arbitrary shape and circular cross-sections. This form implies that the flux rope carries axial current I and axial flux F, so that the respective magnetic field is the curl of the sum of axial and azimuthal vector potentials proportional to I and F, respectively. We expressed the vector potentials in terms of modified Biot–Savart laws, whose kernels are regularized at the axis in such a way that, when the axis is straight, these laws define a cylindrical force-free flux rope with a parabolic profile for the axial current density. For the cases we have studied so far, we determined the shape of the rope axis by following the polarity inversion line of the eruptions’ source region, using observed magnetograms. The height variation along the axis and other flux-rope parameters are estimated by means of potential-field extrapolations. Using this heuristic approach, we were able to construct pre-eruption configurations for the 2009 February 13 and 2011 October 1 CME events. These applications demonstrate the flexibility and efficiency of our new method for energizing pre-eruptive configurations in simulations of CMEs.

Heat flux modeling using ion drift effects in DIII-D H-mode plasmas with resonant magnetic perturbations

DOE PAGES

Wingen, Andreas; Schmitz, Oliver; Evans, Todd E.; ...

2014-01-01

The heat flux patterns measured in low-collisionality DIII-D H-mode plasmas strongly deviate from simultaneously measured CII emission patterns, used as indicator of particle flux, during applied resonant magnetic perturbations. While the CII emission clearly shows typical striations, which are similar to magnetic footprint patterns obtained from vacuum field line tracing, the heat flux is usually dominated by one large peak at the strike point position. The vacuum approximation, which only considers applied magnetic fields and neglects plasma response and plasma effects, cannot explain the shape of the observed heat flux pattern. One possible explanation is the effect of particle drifts.more » This is included in the field line equations and the results are discussed with reference to the measurement. Electrons and ions show di fferent drift motions at thermal energy levels in a guiding center approximation. While electrons hardly deviate from the field lines, ions can drift several centimetres away from field line flux surfaces. A model is presented in which an ion heat flux, based on the ion drift motion from various kinetic energies as they contribute to a thermal Maxwellian distribution, is calculated. The simulated heat flux is directly compared to measurements with a varying edge safety factor q95. This analysis provides evidence for the dominate e ect of high-energy ions in carrying heat from the plasma inside the separatrix to the target. High-energy ions are deposited close to the unperturbed strike line while low-energy ions can travel into the striated magnetic topology.« less

MAGNETIC FLUX SUPPLEMENT TO CORONAL BRIGHT POINTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong

Coronal bright points (BPs) are associated with magnetic bipolar features (MBFs) and magnetic cancellation. Here we investigate how BP-associated MBFs form and how the consequent magnetic cancellation occurs. We analyze longitudinal magnetograms from the Helioseismic and Magnetic Imager to investigate the photospheric magnetic flux evolution of 70 BPs. From images taken in the 193 Å passband of the Atmospheric Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from 2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three processes, namely, emergence, convergence, and local coalescence of the magnetic fluxes. The formation of anmore » MBF can involve more than one of these processes. Out of the 70 cases, flux emergence is the main process of an MBF buildup of 52 BPs, mainly convergence is seen in 28, and 14 cases are associated with local coalescence. For MBFs formed by bipolar emergence, the time difference between the flux emergence and the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr with an average of 1.3 hr. While magnetic cancellation is found in all 70 BPs, it can occur in three different ways: (I) between an MBF and small weak magnetic features (in 33 BPs); (II) within an MBF with the two polarities moving toward each other from a large distance (34 BPs); (III) within an MBF whose two main polarities emerge in the same place simultaneously (3 BPs). While an MBF builds up the skeleton of a BP, we find that the magnetic activities responsible for the BP heating may involve small weak fields.« less

Numerical Simulation of Interacting Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Odstrcil, Dusan; Vandas, Marek; Pizzo, Victor J.; MacNeice, Peter

2003-09-01

A 212-D MHD numerical model is used to investigate the dynamic interaction between two flux ropes (clouds) in a homogeneous magnetized plasma. One cloud is set into motion while the other is initially at rest. The moving cloud generates a shock which interacts with the second cloud. Two cases with different characteristic speeds within the second cloud are presented. The shock front is significantly distorted when it propagates faster (slower) in the cloud with larger (smaller) characteristic speed. Correspondingly, the density behind the shock front becomes smaller (larger). Later, the clouds approach each other and by a momentum exchange they come to a common speed. The oppositely directed magnetic fields are pushed together, a driven magnetic reconnection takes a place, and the two flux ropes gradually coalescence into a single flux rope.

The evolution of a coronal streamer and the photospheric magnetic field

NASA Technical Reports Server (NTRS)

Poland, A. I.; Macqueen, R. M.

1981-01-01

A large equatorial coronal streamer observed in the outer corona grew in brightness and size during successive limb passages between October 6, 1973 and January 10, 1974 (solar rotations 1606-1611). Unlike previous studies of streamers and their photospheric associations, no definite surface feature could be identified in the present case. This suggests that the streamer is associated with the large scale photospheric magnetic field. Comparison of the streamer growth with observed underlying photospheric magnetic flux changes indicated that as the streamer increased in brightness, areal extent, and density, the photospheric magnetic flux decreased. Three possible explanations for the streamer's growth are presented, the conceptually simplest being that the decrease in photospheric field results in an opening of the flux tubes under the streamer, which permits an increase mass flux through the streamer.

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa{sub 2}Cu{sub 3}O{sub 7}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, W.; Heinrich, B.; Zhou, H.

1994-12-31

Mapping of the magnetic flux density B{sub z} (perpendicular to the film plane) for a YBa{sub 2}Cu{sub 3}O{sub 7} thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B{sub z} distributions. From the known sheet magnetization, the tangential (B{sub x,y}) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B{sub x,y}/d, where d is the film thickness. The evolution of flux penetration as a function of applied field willmore » be shown.« less

Portable radiography system using a relativistic electron beam

DOEpatents

Hoeberling, Robert F.

1990-01-01

A portable radiographic generator is provided with an explosive magnetic flux compression generator producing the high voltage necessary to generate a relativistic electron beam. The relativistic electron beam is provided with target materials which generates the desired radiographic pulse. The magnetic flux compression generator may require at least two conventional explosively driven generators in series to obtain a desired output voltage of at least 1 MV. The cathode and anode configuration of the diode are selected to provide a switching action wherein a high impedance load is presented to the magnetic flux compression generator when the high voltage is being generated, and thereafter switching to a low impedance load to generate the relativistic electron beam. Magnetic flux compression generators can be explosively driven and provided in a relatively compact, portable form for use with the relativistic x-ray equipment.

Portable radiography system using a relativistic electron beam

DOEpatents

Hoeberling, R.F.

1987-09-22

A portable radiographic generator is provided with an explosive magnetic flux compression generator producing the high voltage necessary to generate a relativistic electron beam. The relativistic electron beam is provided with target materials which generates the desired radiographic pulse. The magnetic flux compression generator may require at least two conventional explosively driven generators in series to obtain a desired output voltage of at least 1 MV. The cathode and anode configuration of the diode are selected to provide a switching action wherein a high impedance load is presented to the magnetic flux compression generator when the high voltage is being generated, and thereafter switching to a low impedance load to generate the relativistic electron beam. Magnetic flux compression generators can be explosively driven and provided in a relatively compact, portable form for use with the relativistic x-ray equipment. 8 figs.

Electromagnetic Properties Analysis on Hybrid-driven System of Electromagnetic Motor

NASA Astrophysics Data System (ADS)

Zhao, Jingbo; Han, Bingyuan; Bei, Shaoyi

2018-01-01

The hybrid-driven system made of permanent-and electromagnets applied in the electromagnetic motor was analyzed, equivalent magnetic circuit was used to establish the mathematical models of hybrid-driven system, based on the models of hybrid-driven system, the air gap flux, air-gap magnetic flux density, electromagnetic force was proposed. Taking the air-gap magnetic flux density and electromagnetic force as main research object, the hybrid-driven system was researched. Electromagnetic properties of hybrid-driven system with different working current modes is studied preliminary. The results shown that analysis based on hybrid-driven system can improve the air-gap magnetic flux density and electromagnetic force more effectively and can also guarantee the output stability, the effectiveness and feasibility of the hybrid-driven system are verified, which proved theoretical basis for the design of hybrid-driven system.

Modeled ground magnetic signatures of flux transfer events

NASA Technical Reports Server (NTRS)

Mchenry, Mark A.; Clauer, C. Robert

1987-01-01

The magnetic field on the ground due to a small (not greater than 200 km scale size) localized field-aligned current (FAC) system interacting with the ionosphere is calculated in terms of an integral over the ionospheric distribution of FAC. Two different candidate current systems for flux transfer events (FTEs) are considered: (1) a system which has current flowing down the center of a cylindrical flux tube with a return current uniformly distributed along the outside edge; and (2) a system which has upward current on one half of the perimeter of a cylindrical flux tube with downward current on the opposite half. The peak magnetic field on the ground is found to differ by a factor of 2 between the two systems, and the magnetic perturbations are in different directions depending on the observer's position.

Asymmetric lasing at spectral singularities

NASA Astrophysics Data System (ADS)

Jin, L.

2018-03-01

Scattering coefficients can diverge at spectral singularities. In such situation, the stationary solution becomes a laser solution with outgoing waves only. We explore a parity-time (PT )-symmetric non-Hermitian two-arm Aharonov-Bohm interferometer consisting of three coupled resonators enclosing synthetic magnetic flux. The synthetic magnetic flux does not break the PT symmetry, which protects the symmetric transmission. The features and conditions of symmetric, asymmetric, and unidirectional lasing at spectral singularities are discussed. We elucidate that lasing affected by the interference is asymmetric; asymmetric lasing is induced by the interplay between the synthetic magnetic flux and the system's non-Hermiticity. The product of the left and right transmissions is equal to that of the reflections. Our findings reveal that the synthetic magnetic flux affects light propagation, and the results can be applied in the design of lasing devices.

On the structure and stability of magnetic tower jets

DOE PAGES

Huarte-Espinosa, M.; Frank, A.; Blackman, E. G.; ...

2012-09-05

Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales <~ 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models,more » the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Here, unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.« less

Reconstruction of flux coordinates from discretized magnetic field maps

NASA Astrophysics Data System (ADS)

Predebon, I.; Momo, B.; Suzuki, Y.; Auriemma, F.

2018-04-01

We provide a simple method to build a straight field-line coordinate system from discretized (Poincaré) magnetic field maps. The method is suitable for any plasma domain with nested flux surfaces, including magnetic islands. Illustrative examples are shown for tokamak, heliotron, and reversed-field-pinch plasmas with m = 1 islands.

Recycling of the Solar Corona's Magnetic Field

NASA Astrophysics Data System (ADS)

Close, R. M.; Parnell, C. E.; Longcope, D. W.; Priest, E. R.

2004-09-01

Magnetic fields play a dominant role in the atmospheres of the Sun and other Sun-like stars. Outside sunspot regions, the photosphere of the so-called quiet Sun contains myriads of small-scale magnetic concentrations, with strengths ranging from the detection limit of ~1016 Mx up to ~3×1020 Mx. The tireless motion of these magnetic flux concentrations, along with the continual appearance and disappearance of opposite-polarity pairs of fluxes, releases a substantial amount of energy that may be associated with a whole host of physical processes in the solar corona, not least the enigma of coronal heating. We find here that the timescale for magnetic flux to be remapped in the quiet-Sun corona is, surprisingly, only 1.4 hr (around 1/10 of the photospheric flux recycling time), implying that the quiet-Sun corona is far more dynamic than previously thought. Besides leading to a fuller understanding of the origins of magnetically driven phenomena in our Sun's corona, such a process may also be crucial for the understanding of stellar atmospheres in general.

Soft magnetic characteristics of laminated magnetic block cores assembled with a high Bs nanocrystalline alloy

NASA Astrophysics Data System (ADS)

Yao, Atsushi; Inoue, Masaki; Tsukada, Kouhei; Fujisaki, Keisuke

2018-05-01

This paper focuses on an evaluation of core losses in laminated magnetic block cores assembled with a high Bs nanocrystalline alloy in high magnetic flux density region. To discuss the soft magnetic properties of the high Bs block cores, the comparison with amorphous (SA1) block cores is also performed. In the high Bs block core, both low core losses and high saturation flux densities Bs are satisfied in the low frequency region. Furthermore, in the laminated block core made of the high Bs alloy, the rate of increase of iron losses as a function of the magnetic flux density remains small up to around 1.6 T, which cannot be realized in conventional laminated block cores based on amorphous alloy. The block core made of the high Bs alloy exhibits comparable core loss with that of amorphous alloy core in the high-frequency region. Thus, it is expected that this laminated high Bs block core can achieve low core losses and high saturation flux densities in the high-frequency region.

Resistance to Change and Relapse of Observing

ERIC Educational Resources Information Center

Thrailkill, Eric A.; Shahan, Timothy A.

2012-01-01

Four experiments examined relapse of extinguished observing behavior of pigeons using a two-component multiple schedule of observing-response procedures. In both components, unsignaled periods of variable-interval (VI) food reinforcement alternated with extinction and observing responses produced stimuli associated with the availability of the VI…

Pedestrian crosswalk case studies : Sacramento, California; Richmond, Virginia; Buffalo, New York; Stillwater, Minnesota

DOT National Transportation Integrated Search

2001-08-01

The objective of this research was to determine the effect of crosswalk markings on driver and pedestrian behavior at unsignalized intersections. A before/after evaluation of crosswalk markings was conducted at 11 locations in 4 U.S. cities. Behavior...

Development of left-turn lane guidelines for signalized and unsignalized intersections.

DOT National Transportation Integrated Search

2004-01-01

It is generally accepted that the level of service (LOS) at intersections significantly affects the overall LOS of the road system. It is also known that the LOS at an intersection can be adversely affected by frequently allowing left-turning vehicle...

L&D Manual Turn Lane Storage Validation/Update

DOT National Transportation Integrated Search

2012-08-01

Queuing occurs at intersections mostly due to overflow or inadequacy of turn bays. The ODOT L&D : Manual Volume 1 has storage requirements for both signalized and unsignalized intersections. Figures : 401-9E and 401-10E of the L&D Manual provide the ...

Dynamic Processes of the Solar Wind: Small Scale Magnetic Flux Ropes and Energetic Particles

NASA Astrophysics Data System (ADS)

Thompson, S. W.; le Roux, J. A.; Hu, Q.

2017-12-01

Magnetic flux ropes are twisted magnetic field lines that have two defining components known as the axial and azimuthal components representing its magnetic field. Flux ropes come in two distinct sizes of large scale and small scale with the flux ropes of interest being the small scale type. Small scale flux ropes can last from a few minutes to hours with a size of .001 AU to .01 AU. To identify and study these small scale flux ropes, the ARTEMIS satellite which is composed of the probes THEMIS B and C was utilized along with the ACE satellite. Based off the IP shock database, three major events recorded by the ACE satellite were selected and used as a reference point to identify the same shocks within the ARTEMIS data. The three events were selected when the sun was in solar maximum and the location of the probes THEMIS B and C were outside of the bow shock and magnetotail of the Earth. The three events were on May 17,2013, May 31,2013, and June 30,2013 during solar cycle 24. The in-situ measurements gathered from the ARTEMIS mission using the SST, ESA, and FGM instrumentations looked at the particle energy flux, density, temperature, velocity, and magnetic field parameters. These parameters will be used to identify downstream flux-rope activity and to look for associated enhanced energetic particle fluxes as an indication for particle acceleration by these structures. As a way for comparison, in-situ measurements of the energy flux from the ACE satellite EPAM instrumentation using the LEMS120 telescope were taken to help identify high-energy ions in MeV for each of the three events. Preliminary results suggest that energetic particle fluxes peak behind the shocks in the vicinity of small-scale flux ropes, and that these results can potentially be explained by a theory combining diffusive shock acceleration with flux-rope acceleration. More investigation and data analysis will be done to see if this theory does in fact hold true for the data gathered.

Optimization of magnetic flux density for fast MREIT conductivity imaging using multi-echo interleaved partial fourier acquisitions.

PubMed

Chauhan, Munish; Jeong, Woo Chul; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

2013-08-27

Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive method for visualizing the internal conductivity and/or current density of an electrically conductive object by externally injected currents. The injected current through a pair of surface electrodes induces a magnetic flux density distribution inside the imaging object, which results in additional magnetic flux density. To measure the magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels out the systematic artifacts accumulated in phase signals and also reduces the random noise effect by doubling the measured magnetic flux density signal. For practical applications of in vivo MREIT, it is essential to reduce the scan duration maintaining spatial-resolution and sufficient contrast. In this paper, we optimize the magnetic flux density by using a fast gradient multi-echo MR pulse sequence. To recover the one component of magnetic flux density Bz, we use a coupled partial Fourier acquisitions in the interleaved sense. To prove the proposed algorithm, we performed numerical simulations using a two-dimensional finite-element model. For a real experiment, we designed a phantom filled with a calibrated saline solution and located a rubber balloon inside the phantom. The rubber balloon was inflated by injecting the same saline solution during the MREIT imaging. We used the multi-echo fast low angle shot (FLASH) MR pulse sequence for MRI scan, which allows the reduction of measuring time without a substantial loss in image quality. Under the assumption of a priori phase artifact map from a reference scan, we rigorously investigated the convergence ratio of the proposed method, which was closely related with the number of measured phase encode set and the frequency range of the background field inhomogeneity. In the phantom experiment with a partial Fourier acquisition, the total scan time was less than 6 seconds to measure the magnetic flux density Bz data with 128×128 spacial matrix size, where it required 10.24 seconds to fill the complete k-space region. Numerical simulation and experimental results demonstrated that the proposed method reduces the scanning time and provides the recovered Bz data comparable to what we obtained by measuring complete k-space data.

Explicitly Representing the Solvation Shell in Continuum Solvent Calculations

PubMed Central

Svendsen, Hallvard F.; Merz, Kenneth M.

2009-01-01

A method is presented to explicitly represent the first solvation shell in continuum solvation calculations. Initial solvation shell geometries were generated with classical molecular dynamics simulations. Clusters consisting of solute and 5 solvent molecules were fully relaxed in quantum mechanical calculations. The free energy of solvation of the solute was calculated from the free energy of formation of the cluster and the solvation free energy of the cluster calculated with continuum solvation models. The method has been implemented with two continuum solvation models, a Poisson-Boltzmann model and the IEF-PCM model. Calculations were carried out for a set of 60 ionic species. Implemented with the Poisson-Boltzmann model the method gave an unsigned average error of 2.1 kcal/mol and a RMSD of 2.6 kcal/mol for anions, for cations the unsigned average error was 2.8 kcal/mol and the RMSD 3.9 kcal/mol. Similar results were obtained with the IEF-PCM model. PMID:19425558

Signed-negabinary-arithmetic-based optical computing by use of a single liquid-crystal-display panel.

PubMed

Datta, Asit K; Munshi, Soumika

2002-03-10

Based on the negabinary number representation, parallel one-step arithmetic operations (that is, addition and subtraction), logical operations, and matrix-vector multiplication on data have been optically implemented, by use of a two-dimensional spatial-encoding technique. For addition and subtraction, one of the operands in decimal form is converted into the unsigned negabinary form, whereas the other decimal number is represented in the signed negabinary form. The result of operation is obtained in the mixed negabinary form and is converted back into decimal. Matrix-vector multiplication for unsigned negabinary numbers is achieved through the convolution technique. Both of the operands for logical operation are converted to their signed negabinary forms. All operations are implemented by use of a unique optical architecture. The use of a single liquid-crystal-display panel to spatially encode the input data, operational kernels, and decoding masks have simplified the architecture as well as reduced the cost and complexity.

Generalization of Clustering Coefficients to Signed Correlation Networks

PubMed Central

Costantini, Giulio; Perugini, Marco

2014-01-01

The recent interest in network analysis applications in personality psychology and psychopathology has put forward new methodological challenges. Personality and psychopathology networks are typically based on correlation matrices and therefore include both positive and negative edge signs. However, some applications of network analysis disregard negative edges, such as computing clustering coefficients. In this contribution, we illustrate the importance of the distinction between positive and negative edges in networks based on correlation matrices. The clustering coefficient is generalized to signed correlation networks: three new indices are introduced that take edge signs into account, each derived from an existing and widely used formula. The performances of the new indices are illustrated and compared with the performances of the unsigned indices, both on a signed simulated network and on a signed network based on actual personality psychology data. The results show that the new indices are more resistant to sample variations in correlation networks and therefore have higher convergence compared with the unsigned indices both in simulated networks and with real data. PMID:24586367

Estimation of Critical Gap Based on Raff's Definition

PubMed Central

Guo, Rui-jun; Wang, Xiao-jing; Wang, Wan-xiang

2014-01-01

Critical gap is an important parameter used to calculate the capacity and delay of minor road in gap acceptance theory of unsignalized intersections. At an unsignalized intersection with two one-way traffic flows, it is assumed that two events are independent between vehicles' arrival of major stream and vehicles' arrival of minor stream. The headways of major stream follow M3 distribution. Based on Raff's definition of critical gap, two calculation models are derived, which are named M3 definition model and revised Raff's model. Both models use total rejected coefficient. Different calculation models are compared by simulation and new models are found to be valid. The conclusion reveals that M3 definition model is simple and valid. Revised Raff's model strictly obeys the definition of Raff's critical gap and its application field is more extensive than Raff's model. It can get a more accurate result than the former Raff's model. The M3 definition model and revised Raff's model can derive accordant result. PMID:25574160

Estimation of critical gap based on Raff's definition.

PubMed

Guo, Rui-jun; Wang, Xiao-jing; Wang, Wan-xiang

2014-01-01

Critical gap is an important parameter used to calculate the capacity and delay of minor road in gap acceptance theory of unsignalized intersections. At an unsignalized intersection with two one-way traffic flows, it is assumed that two events are independent between vehicles' arrival of major stream and vehicles' arrival of minor stream. The headways of major stream follow M3 distribution. Based on Raff's definition of critical gap, two calculation models are derived, which are named M3 definition model and revised Raff's model. Both models use total rejected coefficient. Different calculation models are compared by simulation and new models are found to be valid. The conclusion reveals that M3 definition model is simple and valid. Revised Raff's model strictly obeys the definition of Raff's critical gap and its application field is more extensive than Raff's model. It can get a more accurate result than the former Raff's model. The M3 definition model and revised Raff's model can derive accordant result.

Observation of the magnetic flux and three-dimensional structure of skyrmion lattices by electron holography.

PubMed

Park, Hyun Soon; Yu, Xiuzhen; Aizawa, Shinji; Tanigaki, Toshiaki; Akashi, Tetsuya; Takahashi, Yoshio; Matsuda, Tsuyoshi; Kanazawa, Naoya; Onose, Yoshinori; Shindo, Daisuke; Tonomura, Akira; Tokura, Yoshinori

2014-05-01

Skyrmions are nanoscale spin textures that are viewed as promising candidates as information carriers in future spintronic devices. Skyrmions have been observed using neutron scattering and microscopy techniques. Real-space imaging using electrons is a straightforward way to interpret spin configurations by detecting the phase shifts due to electromagnetic fields. Here, we report the first observation by electron holography of the magnetic flux and the three-dimensional spin configuration of a skyrmion lattice in Fe(0.5)Co(0.5)Si thin samples. The magnetic flux inside and outside a skyrmion was directly visualized and the handedness of the magnetic flux flow was found to be dependent on the direction of the applied magnetic field. The electron phase shifts φ in the helical and skyrmion phases were determined using samples with a stepped thickness t (from 55 nm to 510 nm), revealing a linear relationship (φ = 0.00173 t). The phase measurements were used to estimate the three-dimensional structures of both the helical and skyrmion phases, demonstrating that electron holography is a useful tool for studying complex magnetic structures and for three-dimensional, real-space mapping of magnetic fields.

New color-magnetic defects in dense quark matter

NASA Astrophysics Data System (ADS)

Haber, Alexander; Schmitt, Andreas

2018-06-01

Color-flavor locked (CFL) quark matter expels color-magnetic fields due to the Meissner effect. One of these fields carries an admixture of the ordinary abelian magnetic field and therefore flux tubes may form if CFL matter is exposed to a magnetic field, possibly in the interior of neutron stars or in quark stars. We employ a Ginzburg–Landau approach for three massless quark flavors, which takes into account the multi-component nature of color superconductivity. Based on the weak-coupling expressions for the Ginzburg–Landau parameters, we identify the regime where CFL is a type-II color superconductor and compute the radial profiles of different color-magnetic flux tubes. Among the configurations without baryon circulation we find a new solution that is energetically preferred over the flux tubes previously discussed in the literature in the parameter regime relevant for compact stars. Within the same setup, we also find a new defect in the 2SC phase, namely magnetic domain walls, which emerge naturally from the previously studied flux tubes if a more general ansatz for the order parameter is used. Color-magnetic defects in the interior of compact stars allow for sustained deformations of the star, potentially strong enough to produce detectable gravitational waves.

ON POLAR MAGNETIC FIELD REVERSAL AND SURFACE FLUX TRANSPORT DURING SOLAR CYCLE 24

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xudong; Todd Hoeksema, J.; Liu, Yang

As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33-2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in 2013 October; the northernmore » and southern polar fields (mean above 60° latitude) reversed in 2012 November and 2014 March, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR tilt, higher total AR flux, or slower mid-latitude near-surface meridional flow, while exceptions occur during low magnetic activity. In particular, the AR flux and the mid-latitude poleward flow speed exhibit a clear anti-correlation. We discuss how these features can be explained in a surface flux transport process that includes a field-dependent converging flow toward the ARs, a characteristic that may contribute to solar cycle variability.« less

An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field

NASA Technical Reports Server (NTRS)

Riley, Pete

2007-01-01

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

Non-kinematic Flux-transport Dynamos Including the Effects of Diffusivity Quenching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ichimura, Chiaki; Yokoyama, Takaaki

2017-04-10

Turbulent magnetic diffusivity is quenched when strong magnetic fields suppress turbulent motion in a phenomenon known as diffusivity quenching. Diffusivity quenching can provide a mechanism for amplifying magnetic field and influencing global velocity fields through Lorentz force feedback. To investigate this effect, we conducted mean field flux-transport dynamo simulations that included the effects of diffusivity quenching in a non-kinematic regime. We found that toroidal magnetic field strength is amplified by up to approximately 1.5 times in the convection zone as a result of diffusivity quenching. This amplification is much weaker than that in kinematic cases as a result of Lorentzmore » force feedback on the system’s differential rotation. While amplified toroidal fields lead to the suppression of equatorward meridional flow locally near the base of the convection zone, large-scale equatorward transport of magnetic flux via meridional flow, which is the essential process of the flux-transport dynamo, is sustainable in our calculations.« less

MAGNETIC FLUX TUBE INTERCHANGE AT THE HELIOPAUSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florinski, V., E-mail: vaf0001@uah.edu

2015-11-01

The magnetic field measured by Voyager 1 prior to its heliocliff encounter on 2012.65 showed an unexpectedly complex transition from the primarily azimuthal inner-heliosheath field to the draped interstellar field tilted by some 20° to the nominal azimuthal direction. Most prominent were two regions of enhanced magnetic field strength depleted in energetic charged particles of heliospheric origin. These regions were interpreted as magnetic flux tubes connected to the outer heliosheath that provided a path for the particles to escape. Despite large increases in strength, the field’s direction did not change appreciably at the boundaries of these flux tubes. Rather, themore » field’s direction changed gradually over several months prior to the heliocliff crossing. It is shown theoretically that the heliopause, as a pressure equilibrium layer, can become unstable to interchange of magnetic fields between the inner and the outer heliosheaths. The curvature of magnetic field lines and the anti-sunward gradient in plasma kinetic pressure provide conditions favorable for an interchange. Magnetic shear between the heliosheath and the interstellar fields reduces the growth rates, but does not fully stabilize the heliopause against perturbations propagating in the latitudinal direction. The instability could create a transition layer permeated by magnetic flux tubes, oriented parallel to each other and alternately connected to the heliosheath or the interstellar regions.« less

A Comparison of Analytical and Experimental Data for a Magnetic Actuator

NASA Technical Reports Server (NTRS)

Groom, Nelson J.; Bloodgood, V. Dale, Jr.

2000-01-01

Theoretical and experimental force-displacement and force-current data are compared for two configurations of a simple horseshoe, or bipolar, magnetic actuator. One configuration utilizes permanent magnet wafers to provide a bias flux and the other configuration has no source of bias flux. The theoretical data are obtained from two analytical models of each configuration. One is an ideal analytical model which is developed under the following assumptions: (1) zero fringing and leakage flux, (2) zero actuator coil mmf loss, and (3) infinite permeability of the actuator core and suspended element flux return path. The other analytical model, called the extended model, is developed by adding loss and leakage factors to the ideal model. The values of the loss and leakage factors are calculated from experimental data. The experimental data are obtained from a magnetic actuator test fixture, which is described in detail. Results indicate that the ideal models for both configurations do not match the experimental data very well. However, except for the range around zero force, the extended models produce a good match. The best match is produced by the extended model of the configuration with permanent magnet flux bias.

Plasma Transport and Magnetic Flux Circulation in Saturn's Magnetosphere

NASA Astrophysics Data System (ADS)

Neupane, B. R.; Delamere, P. A.; Ma, X.; Wilson, R. J.

2017-12-01

Radial transport of plasma in the rapidly rotating magnetospheres is an important dynamical process. Radial transport is due to the centrifugally driven interchange instability and magnetodisc reconnection, allowing net mass to be transported outward while conserving magnetic flux. Using Cassini Plasma Spectrometer instrument (CAPS) data products (e.g., Thomsen et al., [2010]; Wilson et al., [2017]) we estimate plasma mass and magnetic flux transport rates as functions of radial distance and local time. The physical requirement for zero net magnetic flux transport provides a key benchmark for assessing the validity of our mass transport estimate. We also evaluate magnetodisc stability using a two-dimensional axisymmetric equilibrium model [Caudal, 1986]. Observed local properties (e.g., specific entropy and estimates of flux tube mass and entropy content) are compared with modeled equilibrium conditions such that departures from equilibrium can be correlated with radial flows and local magnetic field structure. Finally, observations of specific entropy indicate that plasma is non-adiabatic heated during transport. However, the values of specific entropy are well organized in inner magnetosphere (i.e. L<10), and become widely scattered in the middle magnetosphere, suggesting that the transport dynamics of the inner and middle magnetosphere are different.

On the generation of magnetohydrodynamic waves in a stratified and magnetized fluid. II - Magnetohydrodynamic energy fluxes for late-type stars

NASA Technical Reports Server (NTRS)

Musielak, Z. E.; Rosner, R.

1988-01-01

Magnetohydrodynamic (MHD) wave energy fluxes for late-type stars are calculated, using previously obtained formulae for the source functions for the generation of MHD waves in a stratified, but otherwise uniform, turbulent atmosphere; the magnetic fields in the wave generation region are assumed to be homogeneous. In contradiction to previous results, it is shown that in this uniform magnetic field case there is no significant increase in the efficiency of MHD wave generation, at least within the theory's limits of applicability. The major results are that the MHD energy fluxes calculated for late-type stars are less than those obtained for compressible modes in the magnetic field-free case, and that these MHD energy fluxes do not vary enough for a given spectral type to explain the observed range of UV and X-ray fluxes from such stars. It is therefore concluded that MHD waves in stellar atmospheres with homogeneous magnetic fields in the wave generation region cannot explain the observed stellar coronal emissions; if such MHD waves are responsible for a significant component of stellar coronal heating, then nonuniform fields within the generation region must be appealed to.

Flux-dependent anti-crossing of resonances in parallel non-coupled double quantum dots

NASA Astrophysics Data System (ADS)

Joe, Yong S.; Hedin, Eric R.; Kim, Jiseok

2008-08-01

We present novel resonant phenomena through parallel non-coupled double quantum dots (QDs) embedded in each arm of an Aharonov-Bohm (AB) ring with magnetic flux passing through its center. The electron transmission through this AB ring with each QD formed by two short-range potential barriers is calculated using a scattering matrix at each junction and a transfer matrix in each arm. We show that as the magnetic flux modulates, a distortion of the grid-like square transmission occurs and an anti-crossing of the resonances appears. Hence, the modulation of magnetic flux in this system can have an equivalent effect to the control of inter-dot coupling between the two QDs.

Active Region Jets II: Triggering and Evolution of Violent Jets

NASA Astrophysics Data System (ADS)

Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David; Panesar, Navdeep K.; Martinez, Francisco

2017-08-01

We study a series of X-ray-bright, rapidly evolving active-region coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT, SDO/AIA and HMI, and IRIS/SJ data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets (Sterling et al. 2016, ApJ, 821, 100). The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ˜<2‧‧) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2015, Nature, 523, 437). For some jets strands are difficult/ impossible to detect, perhaps due to their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ~1.5×10^19 Mx/hr. An average flux of ~5×10^18 Mx canceled prior to each episode, arguably building up ~10^28—10^29 ergs of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption buildup and triggering of at least many jets in active regions, quiet regions, and coronal holes.

Observing Flux Rope Formation During the Impulsive Phase of a Solar Eruption

NASA Astrophysics Data System (ADS)

Cheng, Xin; Zhang, J.; Yang, L.; Ding, M.

2011-05-01

Magnetic flux rope is believed to be an important structural component of coronal mass ejections (CMEs). While there exist much observational evidence of the flux rope post the eruption, e.g., as seen in remote-sensing coronagraph images or in-situ solar wind data, the direct observation of flux ropes during CME impulsive phase has been rare or non-exist. In this Letter, we present an unambiguous observation of a flux rope still in the formation phase in the low corona. The CME of interest occurred above the east limb on 2010 November 03 with footpoints partially blocked. The flux rope was seen as a blob of hot plasma in AIA 131 A passband (peak temperature 11 MK) rising from the core of the source active region, rapidly moving outward and stretching upward the surrounding background magnetic field. The stretched magnetic field seemed to curve-in, similar to the classical magnetic reconnection scenario in eruptive flares. The flux rope was also seen as a dark cavity in AIA 211 A passpand (2.0 MK) and 171 A passband (0.6 MK); in these relatively cool temperature bands, a bright rim clearly enclosed the dark cavity. The bright rim likely represents the pile-up of the surrounding coronal plasma compressed by the expanding flux rope. The composite structure seen in AIA multiple temperature bands is very similar to that in the corresponding coronagraph images, which consists of a bright leading edge and a dark cavity, commonly believed to be a flux rope.

Control of the Helicity Content of a Gun-Generated Spheromak by Incorporating a Conducting Shell into a Magnetized Coaxial Plasma Gun

NASA Astrophysics Data System (ADS)

Matsumoto, Tadafumi; Sekiguchi, Jun'ichi; Asai, Tomohiko

In the formation of magnetized plasmoid by a magnetized coaxial plasma gun (MCPG), the magnetic helicity content of the generated plasmoid is one of the critical parameters. Typically, the bias coil to generate a poloidal flux is mounted either on the outer electrode or inside the inner electrode. However, most of the flux generated in the conventional method spreads even radially outside of the formation region. Thus, only a fraction of the total magnetic flux is actually exploited for helicity generation in the plasmoid. In the proposed system, the plasma gun incorporates a copper shell mounted on the outer electrode. By changing the rise time of the discharge bias coil current and the geometrical structure of the shell, the magnetic field structure and its time evolution can be controlled. The effect of the copper shell has been numerically simulated for the actual gun structure, and experimentally confirmed. This may increase the magnetic helicity content results, through increased poloidal magnetic field.

Ultra-sensitive magnetic microscopy with an atomic magnetometer and flux guides

NASA Astrophysics Data System (ADS)

Kim, Young Jin; Savukov, Igor

Many applications in neuroscience, biomedical research, and material science require high-sensitivity, high-resolution magnetometry. In order to meet this need we recently combined a cm-size spin-exchange relaxation-free Atomic Magnetometer (AM) with a flux guide (FG) to produce ultra-sensitive FG-AM magnetic microscopy. The FG serves to transmit the target magnetic flux to the AM thus enhancing both the sensitivity and resolution to tiny magnetic objects. In this talk, we will describe existing and next generation FG-AM devices and present experimental and numerical tests of its sensitivity and resolution. We demonstrate that an optimized FG-AM has sufficient resolution and sensitivity for the detection of a small number of neurons, which would be an important milestone in neuroscience. In addition, as a demonstration of one possible application of the FG-AM device, we conducted high-resolution magnetic imaging of micron-size magnetic particles. We will show that the device can produce clear microscopic magnetic image of 10 μm-size magnetic particles.

Witnessing Solar Rejuvenation

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-09-01

At the end of last year, the Suns large-scale magnetic field suddenly strengthened, reaching its highest value in over two decades. Here, Neil Sheeley and Yi-Ming Wang (both of the Naval Research Laboratory) propose an explanation for why this happened and what it predicts for the next solar cycle.Magnetic StrengtheningUntil midway through 2014, solar cycle 24 the current solar cycle was remarkably quiet. Even at its peak, it averaged only 79 sunspots per year, compared to maximums of up to 190 in recent cycles. Thus it was rather surprising when, toward the end of 2014, the Suns large-scale magnetic field underwent a sudden rejuvenation, with its mean field leaping up to its highest values since 1991 and causing unprecedentedly large numbers of coronal loops to collapse inward.Yet in spite of the increase we observed in the Suns open flux (the magnetic flux leaving the Suns atmosphere, measured from Earth), there was not a significant increase in solar activity, as indicated by sunspot number and the rate of coronal mass ejections. This means that the number of sources of magnetic flux didnt increase so Sheeley and Wang conclude that flux must instead have been emerging from those sources in a more efficient way! But how?Aligned ActivityWSO open flux and the radial component of the interplanetary magnetic field (measures of the magnetic flux leaving the Suns photosphere and heliosphere, respectively), compared to sunspot number (in units of 100 sunspots). A sudden increase in flux is visible after the peak of each of the last four sunspot cycles. Click for a larger view! [Sheeley Wang 2015]The authors show that the active regions on the solar surface in late 2014 lined up in such a way that the emerging flux was enhanced, forming a strong equatorial dipole field that accounts for the sudden rejuvenation observed.Interestingly, this rejuvenation of the Suns open flux wasnt just a one-time thing; similar bursts have occurred shortly after the peak of every sunspot cycle that we have flux measurements for. The authors find that three factors (how the active regions are distributed longitudinally, their sizes, and the contribution of the axisymmetric component of the magnetic field) determine the strength of this rejuvenation. All three of these factors happened to contribute optimally in 2014.As a final note, Sheeley and Wang suggest that the current strength of the axisymmetric component of the magnetic field can be used to provide an early indication of how active the next solar cycle might be. Using this method, they predict that solar cycle 25 will be similar to the current cycle in amplitude.CitationN. R. Sheeley Jr. and Y.-M. Wang2015 ApJ 809 113. doi:10.1088/0004-637X/809/2/113

The Eruption of a Small-scale Emerging Flux Rope as the Driver of an M-class Flare and of a Coronal Mass Ejection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, X. L.; Xue, Z. K.; Wang, J. C.

Solar flares and coronal mass ejections are the most powerful explosions in the Sun. They are major sources of potentially destructive space weather conditions. However, the possible causes of their initiation remain controversial. Using high-resolution data observed by the New Solar Telescope of Big Bear Solar Observatory, supplemented by Solar Dynamics Observatory observations, we present unusual observations of a small-scale emerging flux rope near a large sunspot, whose eruption produced an M-class flare and a coronal mass ejection. The presence of the small-scale flux rope was indicated by static nonlinear force-free field extrapolation as well as data-driven magnetohydrodynamics modeling ofmore » the dynamic evolution of the coronal three-dimensional magnetic field. During the emergence of the flux rope, rotation of satellite sunspots at the footpoints of the flux rope was observed. Meanwhile, the Lorentz force, magnetic energy, vertical current, and transverse fields were increasing during this phase. The free energy from the magnetic flux emergence and twisting magnetic fields is sufficient to power the M-class flare. These observations present, for the first time, the complete process, from the emergence of the small-scale flux rope, to the production of solar eruptions.« less

The reversed and normal flux contributions to axial dipole decay for 1880-2015

NASA Astrophysics Data System (ADS)

Metman, M. C.; Livermore, P. W.; Mound, J. E.

2018-03-01

The axial dipole component of Earth's internal magnetic field has been weakening since at least 1840, an effect widely believed to be attributed to the evolution of reversed flux patches (RFPs). These are regions on the core-mantle boundary (CMB) where the sign of radial flux deviates from that of the dominant sign of hemispheric radial flux. We study dipole change over the past 135 years using the field models gufm1, COV-OBS.x1 and CHAOS-6; we examine the impact of the choice of magnetic equator on the identification of reversed flux, the contribution of reversed and normal flux to axial dipole decay, and how reversed and normal field evolution has influenced the axial dipole. We show that a magnetic equator defined as a null-flux curve of the magnetic field truncated at spherical harmonic degree 3 allows us to robustly identify reversed flux, which we demonstrate is a feature of at least degree 4 or 5. Additionally, our results indicate that the evolution of reversed flux accounts for approximately two-thirds of the decay of the axial dipole, while one third of the decay is attributed to the evolution of the normal field. We find that the decay of the axial dipole over the 20th century is associated with both the expansion and poleward migration of reversed flux patches. In contrast to this centennial evolution, changes in the structure of secular variation since epoch 2000 indicate that poleward migration currently plays a much reduced role in the ongoing dipole decay.

Explosive instability and erupting flux tubes in a magnetized plasma

PubMed Central

Cowley, S. C.; Cowley, B.; Henneberg, S. A.; Wilson, H. R.

2015-01-01

The eruption of multiple flux tubes in a magnetized plasma is proposed as a mechanism for explosive release of energy in plasmas. A significant fraction of the linearly stable isolated flux tubes are shown to be metastable in a box model magnetized atmosphere in which ends of the field lines are embedded in conducting walls. The energy released by destabilizing such field lines can be a large proportion of the gravitational energy stored in the system. This energy can be released in a fast dynamical time. PMID:26339193

The Distribution and Behaviour of Photospheric Magnetic Features

NASA Astrophysics Data System (ADS)

Parnell, C. E.; Lamb, D. A.; DeForest, C. E.

2014-12-01

Over the past two decades enormous amounts of data on the magnetic fields of the solar photosphere have been produced by both ground-based (Kitt Peak & SOLIS), as well as space-based instruments (MDI, Hinode & HMI). In order to study the behaviour and distribution of photospheric magnetic features, efficient automated detection routines need to be utilised to identify and track magnetic features. In this talk, I will discuss the pros and cons of different automated magnetic feature identification and tracking routines with a special focus on the requirements of these codes to deal with the large data sets produced by HMI. By patching together results from Hinode and MDI (high-res & full-disk), the fluxes of magnetic features were found to follow a power-law over 5 orders of magnitude. At the strong flux tail of this distribution, the power law was found to fall off at solar minimum, but was maintained over all fluxes during solar maximum. However, the point of deflection in the power-law distribution occurs at a patching point between instruments and so questions remain over the reasons for the deflection. The feature fluxes determined from the superb high-resolution HMI data covers almost all of the 5 orders of magnitude. Considering both solar mimimum and solar maximum HMI data sets, we investigate whether the power-law over 5 orders of magnitude in flux still holds. Furthermore, we investigate the behaviour of magnetic features in order to probe the nature of their origin. In particular, we analyse small-scale flux emergence events using HMI data to investigate the existence of a small-scale dynamo just below the solar photosphere.

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE

PubMed Central

Amerstorfer, T.; Palmerio, E.; Isavnin, A.; Farrugia, C. J.; Lowder, C.; Winslow, R. M.; Donnerer, J. M.; Kilpua, E. K. J.; Boakes, P. D.

2018-01-01

Abstract Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3‐D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward‐pointing magnetic fields. Here we demonstrate in a proof‐of‐concept way a new approach to predict the southward field B z in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three‐Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun‐Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9–13 July 2013. Three‐Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3‐D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left‐handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation. PMID:29780287

Numerical assessment of low-frequency dosimetry from sampled magnetic fields

NASA Astrophysics Data System (ADS)

Freschi, Fabio; Giaccone, Luca; Cirimele, Vincenzo; Canova, Aldo

2018-01-01

Low-frequency dosimetry is commonly assessed by evaluating the electric field in the human body using the scalar potential finite difference method. This method is effective only when the sources of the magnetic field are completely known and the magnetic vector potential can be analytically computed. The aim of the paper is to present a rigorous method to characterize the source term when only the magnetic flux density is available at discrete points, e.g. in case of field measurements. The method is based on the solution of the discrete magnetic curl equation. The system is restricted to the independent set of magnetic fluxes and circulations of magnetic vector potential using the topological information of the computational mesh. The solenoidality of the magnetic flux density is preserved using a divergence-free interpolator based on vector radial basis functions. The analysis of a benchmark problem shows that the complexity of the proposed algorithm is linearly dependent on the number of elements with a controllable accuracy. The method proposed in this paper also proves to be useful and effective when applied to a real world scenario, where the magnetic flux density is measured in proximity of a power transformer. A 8 million voxel body model is then used for the numerical dosimetric analysis. The complete assessment is completed in less than 5 min, that is more than acceptable for these problems.

Numerical assessment of low-frequency dosimetry from sampled magnetic fields.

PubMed

Freschi, Fabio; Giaccone, Luca; Cirimele, Vincenzo; Canova, Aldo

2017-12-29

Low-frequency dosimetry is commonly assessed by evaluating the electric field in the human body using the scalar potential finite difference method. This method is effective only when the sources of the magnetic field are completely known and the magnetic vector potential can be analytically computed. The aim of the paper is to present a rigorous method to characterize the source term when only the magnetic flux density is available at discrete points, e.g. in case of field measurements. The method is based on the solution of the discrete magnetic curl equation. The system is restricted to the independent set of magnetic fluxes and circulations of magnetic vector potential using the topological information of the computational mesh. The solenoidality of the magnetic flux density is preserved using a divergence-free interpolator based on vector radial basis functions. The analysis of a benchmark problem shows that the complexity of the proposed algorithm is linearly dependent on the number of elements with a controllable accuracy. The method proposed in this paper also proves to be useful and effective when applied to a real world scenario, where the magnetic flux density is measured in proximity of a power transformer. A 8 million voxel body model is then used for the numerical dosimetric analysis. The complete assessment is completed in less than 5 min, that is more than acceptable for these problems.

Battery system and method for sensing and balancing the charge state of battery cells

NASA Technical Reports Server (NTRS)

Davies, Francis J. (Inventor)

2012-01-01

A battery system utilizes a plurality of transformers interconnected with the battery cells. The transformers each have at least one transformer core operable for magnetization in at least a first magnetic state with a magnetic flux in a first direction and a second magnetic state with a magnetic flux in a second direction. The transformer cores retain the first magnetic state and the second magnetic state without current flow through said plurality of transformers. Circuitry is utilized for switching a selected transformer core between the first and second magnetic states to sense voltage and/or balance particular cells or particular banks of cells.

Imprinting superconducting vortex footsteps in a magnetic layer

NASA Astrophysics Data System (ADS)

Brisbois, Jérémy; Motta, Maycon; Avila, Jonathan I.; Shaw, Gorky; Devillers, Thibaut; Dempsey, Nora M.; Veerapandian, Savita K. P.; Colson, Pierre; Vanderheyden, Benoît; Vanderbemden, Philippe; Ortiz, Wilson A.; Nguyen, Ngoc Duy; Kramer, Roman B. G.; Silhanek, Alejandro V.

2016-06-01

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.

Imprinting superconducting vortex footsteps in a magnetic layer

PubMed Central

Brisbois, Jérémy; Motta, Maycon; Avila, Jonathan I.; Shaw, Gorky; Devillers, Thibaut; Dempsey, Nora M.; Veerapandian, Savita K. P.; Colson, Pierre; Vanderheyden, Benoît; Vanderbemden, Philippe; Ortiz, Wilson A.; Nguyen, Ngoc Duy; Kramer, Roman B. G.; Silhanek, Alejandro V.

2016-01-01

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories. PMID:27263660

Novel Transverse Flux Machine for Vehicle Traction Applications: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Z.; Ahmed, A.; Husain, I.

2015-04-02

A novel transverse flux machine topology for electric vehicle traction applications using ferrite magnets is presented in this paper. The proposed transverse flux topology utilizes novel magnet arrangements in the rotor that are similar to the Halbach array to boost flux linkage; on the stator side, cores are alternately arranged around a pair of ring windings in each phase to make use of the entire rotor flux that eliminates end windings. Analytical design considerations and finite-element methods are used for an optimized design of a scooter in-wheel motor. Simulation results from finite element analysis (FEA) show that the motor achievedmore » comparable torque density to conventional rare-earth permanent magnet (PM) machines. This machine is a viable candidate for direct-drive applications with low cost and high torque density.« less

The magnetic topology of the plasmoid flux rope in a MHD-simulation of magnetotail reconnection

NASA Technical Reports Server (NTRS)

Birn, J.; Hesse, M.

1990-01-01

On the basis of a 3D MHD simulation, the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration (including a net dawn-dusk magnetic field component B sub y N is discussed. As a consequence of B sub y N not equalling 0, the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage, topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of an ad hoc plasmoid model.

Evidences on the Existence of Magnetic Flux Rope Before and During a Solar Eruption

NASA Astrophysics Data System (ADS)

Zhang, Jie; Cheng, Xin; Liu, Kai

2013-03-01

We report the observational evidences from the advanced SDO observations that magnetic flux ropes exist before and during solar eruptions. The solar eruption is defined as coronal mass ejection, whether or not associated with a solar flare. Magnetic flux ropes are directly observed as hot EUV channels as seen in the hot AIA 131 (10 MK) and/or AIA 94 (6.4 MK) passbands, but are absent in cool AIA passbands. The fact that flux ropes are only seen in hot temperatures explains their evasion of detection from previous EUV observations, such as SOHO/EIT, TRACE and STEREO/EUVI. The hot channel usually appears as a writhed sigmoidal shape and slowly rises prior to the onset of the impulsive acceleration as well as the onset of the flare. The hot channel transforms into a CME-like semi-circular shape in a continuous way, indicating its trapping or organization by a coherent magnetic structure. The dynamic and thermal properties of flux ropes will also be presented. We further discuss the critical role of flux ropes in CME initiation and subsequent acceleration, in light of contrasting the standard eruptive flare models.

MAGNETAR GIANT FLARES AND THEIR PRECURSORS-FLUX ROPE ERUPTIONS WITH CURRENT SHEETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu Cong; Huang Lei, E-mail: cyu@ynao.ac.cn, E-mail: muduri@shao.ac.cn

2013-07-10

We propose a catastrophic magnetospheric model for magnetar precursors and their successive giant flares. Axisymmetric models of the magnetosphere, which contain both a helically twisted flux rope and a current sheet, are established based on force-free field configurations. In this model, the helically twisted flux rope would lose its equilibrium and erupt abruptly in response to the slow and quasi-static variations at the ultra-strongly magnetized neutron star's surface. In a previous model without current sheets, only one critical point exists in the flux rope equilibrium curve. New features show up in the equilibrium curves for the flux rope when currentmore » sheets appear in the magnetosphere. The causal connection between the precursor and the giant flare, as well as the temporary re-entry of the quiescent state between the precursor and the giant flare, can be naturally explained. Magnetic energy would be released during the catastrophic state transitions. The detailed energetics of the model are also discussed. The current sheet created by the catastrophic loss of equilibrium of the flux rope provides an ideal place for magnetic reconnection. We point out the importance of magnetic reconnection for further enhancement of the energy release during eruptions.« less

Feasibility study of a MgB 2 superconducting magnetic cloak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giunchi, Giovanni; Turrioni, Daniele; Kashikhin, Vladimir

The magnetic shielding capability of bulk MgB 2 hollow cylinders can be fruitfully combined with an external paramagnetic sheath, to tailor the shape of the external magnetic flux lines. By appropriate selection of the external sheath permeability and thickness, it is possible to leave the magnetic flux lines unaltered by the shield (cloaking effect). Preliminary measurements have been performed at 4.2 K on shielding capability of bulk cylinders, which are subjected to axial and transversal magnetic fields up to 5 T. Furthermore, the cloaking conditions have been modeled to find the optimized thickness to realize the cloaking effect. The MgBmore » 2 material of the superconducting shield is also optimized to avoid low-temperature flux jumps, without losing its shielding capability.« less

Feasibility study of a MgB 2 superconducting magnetic cloak

DOE PAGES

Giunchi, Giovanni; Turrioni, Daniele; Kashikhin, Vladimir; ...

2016-04-01

The magnetic shielding capability of bulk MgB 2 hollow cylinders can be fruitfully combined with an external paramagnetic sheath, to tailor the shape of the external magnetic flux lines. By appropriate selection of the external sheath permeability and thickness, it is possible to leave the magnetic flux lines unaltered by the shield (cloaking effect). Preliminary measurements have been performed at 4.2 K on shielding capability of bulk cylinders, which are subjected to axial and transversal magnetic fields up to 5 T. Furthermore, the cloaking conditions have been modeled to find the optimized thickness to realize the cloaking effect. The MgBmore » 2 material of the superconducting shield is also optimized to avoid low-temperature flux jumps, without losing its shielding capability.« less

Magnetic field generation from shear flow in flux ropes

NASA Astrophysics Data System (ADS)

Intrator, T. P.; Sears, J.; Gao, K.; Klarenbeek, J.; Yoo, C.

2012-10-01

In the Reconnection Scaling Experiment (RSX) we have measured out of plane quadrupole magnetic field structure in situations where magnetic reconnection was minimal. This quadrupole out of plane magnetic signature has historically been presumed to be the smoking gun harbinger of reconnection. On the other hand, we showed that when flux ropes bounced instead of merging and reconnecting, this signature could evolve. This can follow from sheared fluid flows in the context of a generalized Ohms Law. We reconstruct a shear flow model from experimental data for flux ropes that have been experimentally well characterized in RSX as screw pinch equilibria, including plasma ion and electron flow, with self consistent profiles for magnetic field, pressure, and current density. The data can account for the quadrupole field structure.

Suppression of 1/f Flux Noise in Superconducting Quantum Circuits

NASA Astrophysics Data System (ADS)

Kumar, Pradeep; Freeland, John; Yu, Clare; Wu, Ruqian; Wang, Zhe; Wang, Hui; Shi, Chuntai; Pappas, David; McDermott, Robert

Low frequency 1/f magnetic flux noise is a dominant contributor to dephasing in superconducting quantum circuits. It is believed that the noise is due to a high density of unpaired magnetic defect states at the surface of the superconducting thin films. We have performed X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) experiments that point to adsorbed molecular oxygen as the dominant source of magnetism in these films. By improving the vacuum environment of our superconducting devices, we have achieved a significant reduction in surface magnetic susceptibility and 1/f flux noise power spectral density. These results open the door to realization of superconducting qubits with improved dephasing times. State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China.

Conditioned Reinforcement Value and Resistance to Change

ERIC Educational Resources Information Center

Shahan, Timothy A.; Podlesnik, Christopher A.

2008-01-01

Three experiments examined the effects of conditioned reinforcement value and primary reinforcement rate on resistance to change using a multiple schedule of observing-response procedures with pigeons. In the absence of observing responses in both components, unsignaled periods of variable-interval (VI) schedule food reinforcement alternated with…

The Fail-Proof Student

ERIC Educational Resources Information Center

Fiamengo, Janice

2013-01-01

In this article, the author comments on an unsigned newspaper piece titled "Helping Talent Rise to the Top," printed in Canada's "Globe and Mail" about a new measure to enhance student well-being at Queen's University in Kingston, Ontario. The "Globe" piece lauds Queen's, a top-ranked Canadian undergraduate school,…

A Thin-Flux-Rope Approximation as a Basis for Modeling of Pre- and Post-Eruptive Magnetic Configurations

NASA Astrophysics Data System (ADS)

Titov, V. S.; Mikic, Z.; Torok, T.; Linker, J.

2016-12-01

Many existing models of solar flares and coronal mass ejections (CMEs) assume a key role of magnetic flux ropes in these phenomena. It is therefore important to have efficient methods for constructing flux-rope configurations consistent with the observed photospheric magnetic data and morphology of CMEs. As our new step in this direction, we propose an analytical formulation that succinctly represents the magnetic field of a thin flux rope, which has an axis of arbitrary shape and a circular cross-section with the diameter slowly varying along the axis. This representation implies also that the flux rope carries axial current I and axial flux F, so that the respective magnetic field is a curl of the sum of toroidal and poloidal vector potentials proportional to I and F, respectively. Each of the two potentials is individually expressed in terms of a modified Biot-Savart law with separate kernels, both regularized at the rope axis. We argue that the proposed representation is flexible enough to be used in MHD simulations for initializing pre-eruptive configurations in the low corona or post-eruptive configurations (interplanetary CMEs) in the heliosphere. We discuss the potential advantages of our approach, and the subsequent steps to be performed, to develop a fully operative and highly competitive method compared to existing methods. Research supported by NSF, NASA's HSR and LWS Programs, and AFOSR.

CHROMOSPHERIC AND CORONAL WAVE GENERATION IN A MAGNETIC FLUX SHEATH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kato, Yoshiaki; Hansteen, Viggo; Gudiksen, Boris

2016-08-10

Using radiation magnetohydrodynamic simulations of the solar atmospheric layers from the upper convection zone to the lower corona, we investigate the self-consistent excitation of slow magneto-acoustic body waves (slow modes) in a magnetic flux concentration. We find that the convective downdrafts in the close surroundings of a two-dimensional flux slab “pump” the plasma inside it in the downward direction. This action produces a downflow inside the flux slab, which encompasses ever higher layers, causing an upwardly propagating rarefaction wave. The slow mode, excited by the adiabatic compression of the downflow near the optical surface, travels along the magnetic field inmore » the upward direction at the tube speed. It develops into a shock wave at chromospheric heights, where it dissipates, lifts the transition region, and produces an offspring in the form of a compressive wave that propagates further into the corona. In the wake of downflows and propagating shock waves, the atmosphere inside the flux slab in the chromosphere and higher tends to oscillate with a period of ν ≈ 4 mHz. We conclude that this process of “magnetic pumping” is a most plausible mechanism for the direct generation of longitudinal chromospheric and coronal compressive waves within magnetic flux concentrations, and it may provide an important heat source in the chromosphere. It may also be responsible for certain types of dynamic fibrils.« less

A model on CME/Flare initiation: Loss of Equilibrium caused by mass loss of quiescent prominences

NASA Astrophysics Data System (ADS)

Miley, George; Chon Nam, Sok; Kim, Mun Song; Kim, Jik Su

2015-08-01

Coronal Mass Ejections (CMEs) model should give an answer to enough energy storage for giant bulk plasma into interplanetary space to escape against the sun’s gravitation and its explosive eruption. Advocates of ‘Mass Loading’ model (e.g. Low, B. 1996, SP, 167, 217) suggested a simple mechanism of CME initiation, the loss of mass from a prominence anchoring magnetic flux rope, but they did not associate the mass loss with the loss of equilibrium. The catastrophic loss of equilibrium model is considered as to be a prospective CME/Flare model to explain sudden eruption of magnetic flux systems. Isenberg, P. A., et al (1993, ApJ, 417, 368)developed ideal magnetohydrodynamic theory of the magnetic flux rope to show occurrence of catastrophic loss of equilibrium according to increasing magnetic flux transported into corona.We begin with extending their study including gravity on prominence’s material to obtain equilibrium curves in case of given mass parameters, which are the strengths of the gravitational force compared with the characteristic magnetic force. Furthermore, we study quasi-static evolution of the system including massive prominence flux rope and current sheet below it to obtain equilibrium curves of prominence’s height according to decreasing mass parameter in a properly fixed magnetic environment. The curves show equilibrium loss behaviors to imply that mass loss result in equilibrium loss. Released fractions of magnetic energy are greater than corresponding zero-mass case. This eruption mechanism is expected to be able to apply to the eruptions of quiescent prominences, which is located in relatively weak magnetic environment with 105 km of scale length and 10G of photospheric magnetic field.

Evidence of Twisted Flux-Tube Emergence in Active Regions

NASA Astrophysics Data System (ADS)

Poisson, M.; Mandrini, C. H.; Démoulin, P.; López Fuentes, M.

2015-03-01

Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic tongues, are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal flux-tubes that form ARs. We develop a new systematic and user-independent method to identify AR tongues. Our method is based on determining and analyzing the evolution of the AR main polarity inversion line (PIL). The effect of the tongues is quantified by measuring the acute angle [ τ] between the orientation of the PIL and the direction orthogonal to the AR main bipolar axis. We apply a simple model to simulate the emergence of a bipolar AR. This model lets us interpret the effect of magnetic tongues on parameters that characterize ARs ( e.g. the PIL inclination and the tilt angles, and their evolution). In this idealized kinematic emergence model, τ is a monotonically increasing function of the twist and has the same sign as the magnetic helicity. We systematically apply our procedure to a set of bipolar ARs (41 ARs) that were observed emerging in line-of-sight magnetograms over eight years. For most of the cases studied, the tongues only have a small influence on the AR tilt angle since tongues have a much lower magnetic flux than the more concentrated main polarities. From the observed evolution of τ, corrected for the temporal evolution of the tilt angle and its final value when the AR is fully emerged, we estimate the average number of turns in the subphotospherically emerging flux-rope. These values for the 41 observed ARs are below unity, except for one. This indicates that subphotospheric flux-ropes typically have a low amount of twist, i.e. highly twisted flux-tubes are rare. Our results demonstrate that the evolution of the PIL is a robust indicator of the presence of tongues and constrains the amount of twist in emerging flux-tubes.

Improving the signal amplitude of meandering coil EMATs by using ribbon soft magnetic flux concentrators (MFC).

PubMed

Dhayalan, R; Satya Narayana Murthy, V; Krishnamurthy, C V; Balasubramaniam, Krishnan

2011-08-01

This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials. Copyright © 2011 Elsevier B.V. All rights reserved.

Unraveling the Complexity of the Evolution of the Sun's Photospheric Magnetic Field

NASA Astrophysics Data System (ADS)

Hathaway, David H.

2016-10-01

Given the emergence of tilted, bipolar active regions, surface flux transport has been shown to reproduce much of the complex evolution of the Sun's photospheric magnetic field. Surface flux is transported by flows in the surface shear layer - the axisymmetric differential rotation and meridional flow and the non-axisymmetric convective motions (granules, supergranules, and giant cells). We have measured these flows by correlation tracking of the magnetic elements themselves, correlation tracking of the Doppler features (supergranules), and by direct Doppler measurements using SDO/HMI data. These measurements fully constrain (with no free parameters) the flows used in our surface flux transport code - the Advective Flux Transport or AFT code. Here we show the up-to-date evolution of these flows, their impact on the detailed evolution of the Sun's photospheric magnetic field, and predictions for what the polar fields will be at the next minimum in 2020.

Nuclear reactor shutdown system

DOEpatents

Bhate, Suresh K.; Cooper, Martin H.; Riffe, Delmar R.; Kinney, Calvin L.

1981-01-01

An inherent shutdown system for a nuclear reactor having neutron absorbing rods affixed to an armature which is held in an upper position by a magnetic flux flowing through a Curie temperature material. The Curie temperature material is fixedly positioned about the exterior of an inner duct in an annular region through which reactor coolant flows. Elongated fuel rods extending from within the core upwardly toward the Curie temperature material are preferably disposed within the annular region. Upon abnormal conditions which result in high neutron flux and coolant temperature, the Curie material loses its magnetic permeability, breaking the magnetic flux path and allowing the armature and absorber rods to drop into the core, thus shutting down the fissioning reaction. The armature and absorber rods are retrieved by lowering the housing for the electromagnet forming coils which create a magnetic flux path which includes the inner duct wall. The coil housing then is raised, resetting the armature.

Method and Apparatus of Implementing a Magnetic Shield Flux Sweeper

NASA Technical Reports Server (NTRS)

Sadleir, John E. (Inventor)

2018-01-01

The present invention relates to a method and apparatus of protecting magnetically sensitive devices with a shield, including: a non-superconducting metal or lower transition temperature (T.sub.c) material compared to a higher transition temperature material, disposed in a magnetic field; means for creating a spatially varying order parameter's |.PSI.(r,T)|.sup.2 in a non-superconducting metal or a lower transition temperature material; wherein a spatially varying order parameter is created by a proximity effect, such that the non-superconducting metal or the lower transition temperature material becomes superconductive as a temperature is lowered, creating a flux-free Meissner state at a center thereof, in order to sweep magnetic flux lines to the periphery.

Studies on equatorial shock formation during plasmaspheric refilling

NASA Technical Reports Server (NTRS)

Singh, N.

1994-01-01

Investigations based on small-scale simulations of microprocesses occurring when a magnetic flux tube refills with a cold plasma are summarized. Results of these investigations are reported in the following attached papers: (1) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: The Role of Ion Beam-Driven Instabilities'; and (2) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: Effects of Magnetically Trapped Hot Plasma'. Other papers included are: 'Interaction of Field-Aligned Cold Plasma Flows with an Equatorially-Trapped Hot Plasma: Electrostatic Shock Formation'; and 'Comparison of Hydrodynamic and Semikinetic Treatments for a Plasma Flow along Closed Field Lines'. A proposal for further research is included.

Demagnetization using a determined estimated magnetic state

DOEpatents

Denis, Ronald J; Makowski, Nathanael J

2015-01-13

A method for demagnetizing comprising positioning a core within the electromagnetic field generated by a first winding until the generated first electrical current is not substantially increasing, thereby determining a saturation current. A second voltage, having the opposite polarity, is then applied across the first winding until the generated second electrical current is approximately equal to the magnitude of the determined saturation current. The maximum magnetic flux within the core is then determined using the voltage across said first winding and the second current. A third voltage, having the opposite polarity, is then applied across the first winding until the core has a magnetic flux equal to approximately half of the determined maximum magnetic flux within the core.

Modelling the Surface Distribution of Magnetic Activity on Sun-Like Stars

NASA Astrophysics Data System (ADS)

Isik, Emre

2018-04-01

With the advent of high-precision space-borne stellar photometry and prospects for direct imaging, it is timely and essential to improve our understanding of stellar magnetic activity in rotational time scales. We present models for 'younger suns' with rotation and flux emergence rates between 1 and 16 times the solar rate. The models provide latitudinal distributions and tilt angles of bipolar magnetic regions, using flux tube rise simulations. Using these emergence patterns, we model the subsequent surface flux transport, to predict surface distributions of star-spots. Based on these models, we present preliminary results from our further modelling of the observed azimuthal magnetic fields, which strengthen for more rapidly rotating Sun-like stars.

Flux transformers made of commercial high critical temperature superconducting wires.

PubMed

Dyvorne, H; Scola, J; Fermon, C; Jacquinot, J F; Pannetier-Lecoeur, M

2008-02-01

We have designed flux transformers made of commercial BiSCCO tapes closed by soldering with normal metal. The magnetic field transfer function of the flux transformer was calculated as a function of the resistance of the soldered contacts. The performances of different kinds of wires were investigated for signal delocalization and gradiometry. We also estimated the noise introduced by the resistance and showed that the flux transformer can be used efficiently for weak magnetic field detection down to 1 Hz.

A linear magnetic motor and generator

NASA Technical Reports Server (NTRS)

Studer, P. A.

1980-01-01

In linear magnetic motor and generator suitable for remote and hostile environments, magnetic forces drive reciprocating shaft along its axis. Actuator shaft is located in center of cylindrical body and may be supported by either contacting or noncontacting bearings. When device operates as bidirectional motor, drive coil selectively adds and subtracts magnetic flux to and from flux paths, producing forces that drive actuator along axis. When actuator is driven by external reciprocating engine, device becomes ac generator.

Development of a vector-tensor system to measure the absolute magnetic flux density and its gradient in magnetically shielded rooms.

PubMed

Voigt, J; Knappe-Grüneberg, S; Gutkelch, D; Haueisen, J; Neuber, S; Schnabel, A; Burghoff, M

2015-05-01

Several experiments in fundamental physics demand an environment of very low, homogeneous, and stable magnetic fields. For the magnetic characterization of such environments, we present a portable SQUID system that measures the absolute magnetic flux density vector and the gradient tensor. This vector-tensor system contains 13 integrated low-critical temperature (LTc) superconducting quantum interference devices (SQUIDs) inside a small cylindrical liquid helium Dewar with a height of 31 cm and 37 cm in diameter. The achievable resolution depends on the flux density of the field under investigation and its temporal drift. Inside a seven-layer mu-metal shield, an accuracy better than ±23 pT for the components of the static magnetic field vector and ±2 pT/cm for each of the nine components of the gradient tensor is reached by using the shifting method.

Development of a vector-tensor system to measure the absolute magnetic flux density and its gradient in magnetically shielded rooms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voigt, J.; Knappe-Grüneberg, S.; Gutkelch, D.

2015-05-15

Several experiments in fundamental physics demand an environment of very low, homogeneous, and stable magnetic fields. For the magnetic characterization of such environments, we present a portable SQUID system that measures the absolute magnetic flux density vector and the gradient tensor. This vector-tensor system contains 13 integrated low-critical temperature (LTc) superconducting quantum interference devices (SQUIDs) inside a small cylindrical liquid helium Dewar with a height of 31 cm and 37 cm in diameter. The achievable resolution depends on the flux density of the field under investigation and its temporal drift. Inside a seven-layer mu-metal shield, an accuracy better than ±23more » pT for the components of the static magnetic field vector and ±2 pT/cm for each of the nine components of the gradient tensor is reached by using the shifting method.« less

Origin and Reduction of 1 / f Magnetic Flux Noise in Superconducting Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, P.; Sendelbach, S.; Beck, M. A.

2016-10-01

Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as 1=fα, with α ≲ 1, and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be reduced by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more thanmore » an order of magnitude and a suppression of 1=f magnetic flux noise power spectral density of up to a factor of 5. These advances open the door to the realization of superconducting qubits with improved quantum coherence.« less

Origin and Reduction of 1 /f Magnetic Flux Noise in Superconducting Devices

NASA Astrophysics Data System (ADS)

Kumar, P.; Sendelbach, S.; Beck, M. A.; Freeland, J. W.; Wang, Zhe; Wang, Hui; Yu, Clare C.; Wu, R. Q.; Pappas, D. P.; McDermott, R.

2016-10-01

Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as 1 /fα, with α ≲1 , and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be reduced by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of 1 /f magnetic flux noise power spectral density of up to a factor of 5. These advances open the door to the realization of superconducting qubits with improved quantum coherence.

Magnetic materials selection for static inverter and converter transformers

NASA Technical Reports Server (NTRS)

Mclyman, C. W. T.

1971-01-01

Different magnetic alloys best suited for high-frequency and high-efficiency applications were comparatively investigated together with an investigation of each alloy's inherent characteristics. One of the characteristics in magnetic materials deterimental in transformer design is the residual flux density, which can be additive on turn-on and cause the transformer to saturate. Investigation of this problem led to the design of a transformer with a very low residual flux. Tests were performed to determine the dc and ac magnetic properties at 2400 Hz using square-wave excitation. These tests were performed on uncut cores, which were then cut for comparison of the gapped and ungapped magnetic properties. The optimum transformer was found to be that with the lowest residual flux and a small amount of air gap in the magnetic material. The data obtained from these tests are described, and the potential uses for the materials are discussed.